Modernized Blucher

Paid commission from @SarcastiCat

From the author:

Laid Down 1907, Commissioned 1909, Sunk (Historically) 1915.

Fictional 1938 Design, Re-Entered Service Late 1940.

Description of Grosser Kreuzer Blucher:

The story of SMS Blucher (II) is relatively well-known, so I won’t expound upon it much here.

SMS Blucher’s life began as “Grosser Kreuzer E” (“Large Cruiser E”), a design first sketched in 1905. The overall design process was quite protracted, lasting a couple of years and considering everything from a slightly improved Scharnhorst-class to larger designs with 24cm (9.45in) guns, but due to cost the 21cm caliber was eventually kept. To increase the 21cm gun’s effectiveness over the Scharnhorst-class’s, the barrel length was increased from 40-caliber to 45-caliber, with 50-caliber single and twin turrets being considered. By the end of the design phase, the ship had grown quite significantly from the previous Scharnhorst-class, and was poised to even receive the relatively new (in the Kaiserliche Marine) steam turbine, but the delay caused by further design was deemed unacceptable, and so the ship was to be constructed with three triple expansion engines instead.

Blucher was ordered in 1906, but was not laid down until February 1907. However, unfortunately, in this period the actual caliber of the British Invincible – the world’s first battlecruiser – became known: 30.5cm (12”). There then became a quite clear disparity between Blucher and this new type of warship. Any chance to change Blucher’s design to meet this new threat had long since passed, as funds had already been approved and authorization given by Kaiser Wilhelm II, so construction proceeded as planned.

Despite the displacement or speed not being significantly different between Blucher and Invincible, and the latter even having thinner belt armor, this new type of warship represented by HMS Invincible and her sisters immediately heralded the end of the Armored Cruiser as an effective warship type worldwide. They would not return until the Treaty Era, and only then in a revised form as “Heavy Cruisers”.

Even still, despite the rapidly approaching obsolescence of Armored Cruisers, SMS Blucher – appropriately considered the last of the Armored Cruiser type – represented the pinnacle of them. Aidan Dodson, author of The Kaiser’s Battlefleet: German Capital Ships 1870-1918, points out that, despite the clear difference in firepower, Blucher had the clear and reasonable potential to have given a good account of herself against the early British battlecruisers, which aside from their significantly increased caliber were hardly a step-up in evolution from Blucher, hull and powerplant-wise. While it is true that Blucher would be sunk by British battlecruisers during her final battle at Dogger Bank, it required approximately 70+ hits (several of them large-caliber from the pursuing battlecruisers) and multiple torpedoes before she capsized – and only then on the surface, taking several additional minutes to sink beneath the surface. During the course of the chase, Blucher had managed to fire back and even inflict damage, though relatively minor when compared to what was wrought by the German battlecruisers steaming with her. I do not think Defence fared nearly as well.

I won’t go further into the battle or SMS Blucher’s service history here, but the Wikipedia article and appropriate books are readily available which will give you more than decent insight into her.

To make a rather rough WW2-esque analogy of the introduction of the Battlecruiser and its effect on the Armored Cruiser type, specifically in the case of Blucher and Invincible, it would be like the difference between USS Des Moines and the Japanese B-65 Super Type A (Large) Cruiser. While Des Moines reasonably represents the pinnacle of Heavy Cruiser design at the time of her introduction, the growing resurgence of the Battlecruiser type (re-imagined in the form of the “Large Cruiser”) in the late 1930s had threatened to run the Heavy Cruiser type into obsolescence before the beginning of the war and the increasing realization of the potential of air power had, in turn, severely dampened interest in big-gun ships of all types. Now that doesn’t mean that Des Moines is incapable of giving a good account of herself against a B-65, as aside from their significantly increased caliber the latter is hardly a step-up in evolution from a Heavy Cruiser, hull and powerplant-wise…and, of course, there are still very many Heavy Cruisers, just as there were Armored Cruisers, which are still around, waiting to be fought against.

BRIEF AU LORE – This modernization project takes place in an alternate universe, and is thus obviously not real. The relevant context of this roughly sketched out AU project – with only passing adherence to logic or reason – is that Imperial Germany wins (or rather, staves off losing) just enough to have a meaningful hand in negotiations. Ultimately, through these protracted negotiations with the Allied powers, Germany gives up (or trades for other, more favorable, items during the negotiations) a rather sizable portion of its fleet – forced to either sell or scrap. As a further measure, vessels under construction or planned for construction were to be scrapped, and the battleship Baden was to be transferred to the Royal Navy for study before being expended as a target (this is what allowed the Kaiserliche Marine to keep Bayern). Negotiations on the size of Germany’s remaining fleet caused the British to develop a version of the Washington Naval Treaty early, and Germany was assigned a maximum capital ship tonnage of 175,000 – in-line with France and Italy. From this, Germany attempted to keep hold of its most usable units, and managed to hold on to Blucher under the premise that she would be de-militarized and either used as a training ship or target ship – but of course, to Germany, this was only ever intended to stand until she could get away with putting the ship back into service.
Regardless of the Kaiserliche Marine, the political situation in post-war Germany was dire. Civil wars erupted immediately after cessation of hostilities, and Social Democrats managed to worm their way into control of the country. Their government was weak, and Germany was on the brink of economic collapse. Things did stabilize, before nosediving in 1929-30.
By the power of mental gymnastics and the magic of “cuz I said so”, the interwar era continues practically the same with no major changes. Hitler takes power in 1933, and the Kriegsmarine begins its rapid expansion in 1935, practically skipping the AGNA. Remaining older battleships and battlecruisers are slated for massive rebuilds where practical (mostly the battlecruisers), as this is projected to be quicker and cheaper than solely new construction. New construction does occur, but it is limited, and only two enlarged versions of “Schwerer Kreuzer” D/E are laid down in 1935. They feature a battery of three triple 28cm guns as a gesture of good will (intended to be up-gunned to 38cm at the first opportunity). Blucher finally has her turn in 1938, and is completed by 1940.
The rebuilds and refits of older vessels was undertaken to provide a sort-of “Home Fleet” for the Kriegsmarine, which would allow more modern units to be freed for longer-ranged duties in the Atlantic.

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Detailed Breakdown of Grosser Kreuzer Blucher (1940):

The design had the following characteristics:

Dimensions: 161.1m (w/l) x 24m

Displacement: ~18,500 tons (full load)

Armor: 180mm Belt (thins to 120-140mm in upper section), 180mm Fore and Aft Belt/60mm Upper, 80mm Bow and Stern/60mm Bow and Stern Upper, 140mm Casemates, 25mm Upper Deck, 25mm Casemate Deck, 60-50-30-70-50 (60-50mm slopes) Armored Deck (Aft->Fwd)

Engines:

12x Wagner boilers / 3x Blohm and Voss turbines (132,000 shp), 3 shafts

Speed: 57km/h (~31kn) (forced) 55km/h (~29.5kn) (maximum rated)

Directors:

1x 7-meter Stereoscopic Main Battery Rangefinder (Foretop)

1x 7-meter Stereoscopic Main Battery Rangefinder (Aft Conning Tower)

1x 6-meter Stereoscopic Main/Secondary Battery Rangefinder (Forward Conning Tower)

2x 7-meter Stereoscopic Main Battery Rangefinders (Turrets No. 1 and 6)

2x 4-meter LA/HA Stereoscopic AAA Battery Directors (Port & Starboard Funnel)

2x 3-meter Stereoscopic Night Rangefinders (Port & Starboard Bridge Deck)

Armaments:

6x2 21cm/45 SK L/45 in Drh. L. C/06 (Modified)

8x1 15cm/48 TK C/36 in MPL C/06 (Modified)

4x2 10.5cm/65 SK C/33 in Dopp. L. C/31d

4x2 3.7cm/83 SK C/30 in Dopp. L. C/30

8x1 2cm/65 C/38 in Sock. L. C/30

2x4 53.3cm Shielded Torpedo Tubes

Seaplanes:

2x Arado Ar-196 A-2

Radars/Sensors:

1x FuMO 22 (Foretop Rangefinder)

TYPOLOGY – While the world typically refers to Blucher and her predecessors as “Armored Cruisers”, their designation was officially “Grosse Kreuzer” (lit. “Large Cruisers”). This type was created to separate them from the “Kleine Kreuzer” (“Small Cruisers”), and could be compared adequately as the separation between Light and Heavy Cruisers of the Treaty Era. The more knowledgeable among you might recognize “Grosse Kreuzer” as the designation for Imperial German “Battlecruisers”, but in reality, the application of the term changed and evolved over the years. Initially it was applied to (functionally) Armored Cruisers, but was then applied to (functionally) Battlecruisers – initially as a cover, but it stuck regardless and became the official designation. Thus, what exactly a “Grosse Kreuzer” is depends principally on the era (and/or what ship specifically) it is being used in reference to.

HULL – As far as changes to the hull go, very little has changed (externally) despite the drastic change to overall appearance. Very early on in the post-war period, Blucher’s ram-style bow was replaced with a more modern type to improve her seakeeping and increase internal volume. [This bow type is based heavily on the one used post-war by the light cruiser Berlin.] However, much inside the hull has changed, including the removal of the hull-mounted torpedo tubes (as a primarily example, but not limited to this) and the conversion of their much-needed real-estate into something much more useful for a warship equipped with relatively modern weapons systems, including modern rangefinders, stabilized AAA and directors, automatic data-transmitting targeting equipment, and new above-water torpedo systems to name a few. Main battery, AA battery, and torpedo battery computer rooms were installed, along with a reserve conning position. Aside from a re-arrangement of Blucher’s guts, a general refurbishment and modernization of the living facilities was undertaken. While much-needed, long-term habitability of the ship remained a poor, and stores for food were rather minimal as a reflection of the intended operational area.

SUPERSTRUCTURE – The changes to Blucher’s superstructure are the most striking by and large, but are not as complex as they seem. To reduce cost and time, especially as the political situation began to take a nosedive in 1938 (that is, during the design and early work phase), it became quite pertinent to at least utilize some of the pre-existing superstructure on the upper deck. Due to Imperial German practice, there wasn’t exactly much to work with at the start, but that also meant there was little that needed to be cleared away. With as little internal space as there was to begin with, and absolutely all of it being allocated to rooms for electronics or other critical new equipment, new room needed to be created somewhere. This was accomplished by increasing the size of the superstructure. The forecastle deck (holding the forward 21cm turret and forward superstructure primarily, and per the original design was connected somewhat tenuously to the aft superstructure/conning tower by a series of catwalks) and the aft superstructure were connected by filling entire midships area out, where possible, to create a singular large superstructure between the aft end of the forward superstructure to the forward end of the aft superstructure. Cutouts in this superstructure provided complete arcs to the four broadside (midships) 21cm turrets. The dimensions of the aft superstructure provided the perfect width, so it was not altered in any significant way. This width on the original superstructure design was intentional, as it allowed the broadside turrets to fire directly astern (or, in the case of the forward end of the ship, forward) while still providing the maximum superstructure width allowable. However, the midships area superstructure (between the forward and aft pair of 21cm broadside turrets) was widened significantly, and ended up closer to the edge of the hull, but was limited from going out to the hull edge completely by the excellent arcs of the midships guns and the need to fit Cutters (boats) port and starboard. This comparatively massive increase in superstructure area allowed for the movement of non-combat-critical spaces from within the hull to the new superstructure spaces. This included the galley, some berthing spaces (some of which were necessary due to the increase in crew size), food storage, office spaces/log rooms, torpedo workshop, DC workshops, and the like.
On the forward superstructure the original conning tower, mast, and searchlight platform - as well as anything else remaining on that deck - were entirely stripped away. This formed the base of the new superstructure, of which was modeled on that of the Admiral Hipper-class [with some specific nods to Kriegsmarine Blucher]. To fit the length of such a large new structure, this required the base to be extended slightly further aft. Despite this extension, the forward superstructure was quite compacted lengthwise, but at least was relatively acceptable in terms of width. This was ultimately deemed acceptable, as it – along with the funnel – helped provide a deceptive silhouette which, at range, had at least the potential to fool enemy lookouts into believing the elderly Armored Cruiser was a member of the Admiral Hipper-class. This specific sort of deceptiveness is not foreign to the Kriegsmarine in the slightest – and that is true in more ways than Hipper’s and Bismarck’s looking alike. Aside from the intentionally deceptive appearance of the superstructure, it also provided the most utility and makes the most extensive use of the available space, though a smaller or older superstructure design might have been, surprisingly, more comfortable and roomier.
Despite superficially looking almost exactly like a Hipper’s, the compacted nature of the superstructure makes itself obvious in the details. Where a Hipper has an enclosed conning station ahead of the forward conning tower, plus an additional length of space ahead of that before reaching the face of the superstructure, Blucher is forced to have this conning station connect directly to the face of the superstructure. And while by 1938 7-meter enclosed rangefinders atop the forward conning tower were now the norm for Hipper design (as seen on Kreuzer J/Prinz Eugen’s design since 1937 and continued in K and L) this had to be downgraded to a simpler 6-meter model like the ones used on Admiral Hipper [and KM Blucher] - though the enclosure remained at least. Aft of this tertiary rangefinder would either be a 3-meter rangefinder or perhaps an AA target giver (ZAG), but the lack of space forced the elimination of these in that location. Instead, the 3-meter rangefinders were displaced to port and starboard (approximately where the 4-meter SL6/8 AAA rangefinders would be on an Admiral Hipper), and a pair of 3.7cm SK C/30 twin mounts is crammed just forward of those. Instead of the ZAG being at this level, a page is taken from the Prinz Eugen with two – one port, one starboard – being placed in the foretop. Undoubtedly the officers and crew will not enjoy the generally cramped space around the forward conning tower. As completed, the Admiral’s Bridge was of the earlier open type, though this would be quickly altered to the closed type to keep the ship in-line with the improvements seen on Admiral Hipper-class ships and other units in the Kriegsmarine. A centerline stabilized searchlight sits above the Admiral’s Bridge, just as it does on most other Kriegsmarine warships.
The funnel was ripped straight from the Admiral Hipper-class [specifically Blucher] and does not differ from it in any recognizable or significant way.
Aft of the funnel is a deckhouse which primarily serves as a boat deck (and provides vertical space so there is working room around the midships broadside 10.5cm guns when they are trained outboard), but also as another means of increasing “internal” volume. Aft of the catapult is a small deck house – practically a hut – where 10.5cm ready ammunition is stored for the aft pair of 10.5cm guns, and as a means of shelter for the ammunition elevators ports which terminate at the deck within the deck house.
The aft superstructure, similarly to the forward superstructure, was completely stripped (before, as stated previously, being expanded forward to connect with the forward superstructure). In place of the four 8.8cm/45 guns and tiny aft conning tower is a new mainmast (with searchlight and signal platform), Deutschland-style aft conning tower, and a comprehensive target giver array along with a pair of 3.7cm/83 SK C/30 twin mounts.
While the Deutschland’s and (initially) Scharnhorst’s had opted for the placement of the mainmast on the searchlight platform immediately behind the funnel, this was a clearly suboptimal arrangement and was rectified on Scharnhorst with intentions to do the same with Gneisenau during her 38cm conversion. The Deutschland-class remained with the older arrangement out of necessity. Scharnhorst’s mainmast combined several functions, including a searchlight platform, signal locker/platform, and even a morse signal lamp. While normally these positions would be split up and arranged around the deck to prevent all of them easily being lost in a single hit (as in Hipper’s, Bismarck’s), Scharnhorst did not have adequate deck space for this - hence the multifunctional nature of the mainmast. Coincidentally, Blucher is similarly lacking deck space, and so it becomes quite clear as to why Scharnhorst’s mast is practically copied in this instance. While a simple pole mast, such as what is seen on Bismarck or Tirpitz, would appear to have been even more space-efficient on the surface, those masts are not load-bearing structures like those of the Admiral Hipper-class or Scharnhorst, which must support the weight of heavy searchlights and platforms, thus requiring support struts. One cannot have all of that weight on a mast without proper support
Considerable time and funds were saved by simply building off of and integrating portions of the original superstructure, cutting the need to start with a new superstructure from scratch or change anything significantly. Instead, the yard could focus on simply “adding on” to what is already there.

MACHINERY PLANT – Initially it was not seen as necessary to improve Blucher’s machinery plant, and several early designs and their variations were drawn under the assumption that little to nothing would change in that area. However, surely, as if there was any doubt, the scope of the design began to grow as weak points were identified, and possible solutions were voiced at meetings or in correspondence between the various offices within the OKM. At some point, someone in Office K realized that the 110,000 shaft horsepower plant of the Admiral Hipper-class could fit comfortably within the original spaces taken by Blucher’s Imperial-era boilers and triple expansion engines, and the idea took hold despite initial pushback.
Just as in the Kriegsmarine, speed was an important consideration for the Kaiserliche Marine, and doubly so for Grosse Kreuzer. Often, to achieve high speeds, a significant length of the citadel was utilized for the ship’s machinery, which tended to leave the ends rather sparse in terms of space and thus long-term habitability. In some designs even seakeeping was sacrificed. All of this was intentional; the High Seas Fleet was a force primarily intended for North and Baltic Sea service – not far-flung Atlantic operations, and ships were not expected to be out at sea for more than a couple of weeks at a time. This does, however, have the benefit of enabling several German ships from the Imperial era to be quite easily refit – for local use, at least.
Despite constant refurbishment, transition to oil-firing, and careful care over the years, nothing stopped the march of time and the wear-and-tear it causes on machinery. By 1938, Blucher’s plant had been in continuous use for nearly 30 years; she could no longer come anywhere near her original top speed of 25.4 knots and was, in effect, limited to speeds below 20 knots. Although never designed to go far from Germany, close and near losses – avoidable losses – had still managed to occur in the past due to a lack of necessary speed. In spite of being 30 years old, Blucher was, at least, still a very well-armed and well-armored platform (especially against cruisers), and though the hull form did not allow for significant speed, a sharp improvement was necessary if the ship was to be made into anything resembling a useful and well-balanced pseudo-heavy cruiser, as was imagined. Since the armament and hull were worth keeping the ship in active service for, it became no great leap to justify a complete replacement of Blucher’s machinery.
And so a series of twelve boilers and three geared steam turbines replaced the original 18 boilers and three four-cylinder triple expansion engines. Although individual components of steam systems had not gotten truly smaller, steam technology as a whole had advanced quite far in the interwar period, and as a result the amount of space it required to generate the same amount of power had shrunk considerably. Although the complete width of the citadel had been taken up, several meters of length had been freed up as spaces for auxiliary equipment, necessary to meet the massive leap in electrical power demand as well as for damage control/dewatering. Fuel capacity remained at a minimum due to the limited distances Blucher was expected to travel – typically not outside of the Baltic or North Sea.
The replacement of the Blucher’s machinery ended up being the most expensive and time-consuming portion of the ship’s modernization. This was despite using a known design and arrangement - even the same funnel type – it didn’t matter. Still, this did at least have the benefit of saving considerable design work, and the components and assembly were familiar to yard workers who had, or still were, working on Admiral Hipper-class cruisers.
In spite of the less-than-optimal hull form, Blucher still managed to hit 31 knots at overload power (~132,000 shp) and maintained a solid 29.5 knots at rated maximum power (110,000 shp). While it was a step or two away from the 32-32.5 knots that could be expected from a Hipper, it was a significant leap from the much-reduced interwar speed of 20 knots (often 18 knots, as hitting around these speeds caused the ship to vibrate horribly…at best) and enabled the elderly Armored Cruiser to move at respectable speed with newer cruisers and capital ships.
[If you remain skeptical about the fitting of the plant, then not to worry; I’ve already done the measuring for you. You’re welcome.]

Boiler Spaces (Blucher): 44.3m
Minimum Length for Boilers (PE): 35m
Remaining Length for Other Purposes: 9.3m

Conclusion: More than enough space for boilers + additional spaces, intermixed or forward of where the boilers would usually end).

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Width of Boiler Rooms at Fr. 59 (Blucher): 16.1m
Width of Boiler Rooms at Fr. 64 (Blucher): 16m
Width of Boiler Rooms at Fr. 75 (Blucher): 15.9m
Width of Boiler Rooms at Fr. 79 (Blucher): 15.2m
Width of Boiler Rooms at Fr. 83 (Blucher): 14.2m

Width of Boiler Rooms (All) (PE): 14.5m

Conclusion: In all spaces except the very forward BR - which will never be reached - the width is more than enough.

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Length of 1 TEE Room (Blucher): 12.55m
Length of 2 TEE Rooms (Blucher): 25.1m

Length of 1 TB Room (PE): 12.5m
Length of 2 TB Rooms (PE): 25m

Conclusion: Nearly 1:1 fit, will be no problem.

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Width of 1 TEE Room (Blucher): 8.1m
Width of 2 TEE Rooms (Blucher): 16m

Width of 1 TB Room (PE): 10.7m
Width of 1 TB Room (Fwd, Splitting TB Rm 2/3 in Half) (PE): 7.1m (<-- Minimum Req Space for 1 TB Room, not 10.7m).
Width of 2 TB Room (PE): 14.42m

Conclusion: More than enough space for necessary turbine rooms.

All widths on Blucher are to torpedo bulkhead.

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Height of Citadel (Top of Double Bottom) (Blucher): 7.7m

Height of Citadel (Top of Double Bottom) (PE): 6.3m

Conclusion: Way more than enough height.

ARMOR – Blucher featured a rather complex armor system with many varied thicknesses. Given the complexity, I won’t delve into the armor much here, as Wikipedia (as well as relevant plans, if you know where to find them) already gives an accurate enough picture of the armor. That armor, which is briefly touched upon in the “detailed breakdown” section above, was already more than enough to be practically immune to 15.2cm (6”)-caliber shellfire at combat ranges, and was strongly resistant to most 20.3cm (8”)-caliber fire. As such it was not altered, improved, or reduced in any significant way during the modernization.

OPTICS – In keeping with Kriegsmarine practice, the suite of optical equipment is vast. The primary rangefinders are two 7-meter models in the early rounded housing seen on Admiral Hipper [and KM Blucher], with one being located in the foretop and one atop the aft conning tower. A tertiary 6-meter rangefinder in a circular enclosed housing with a domed roof – the same type seen on Prinz Eugen – is located atop the forward conning tower. A 7-meter rangefinder would typically be used at the time of Blucher’s design phase, but a 6-meter rangefinder had to be substituted due to its reduced arc diameter. Two 4-meter SL8 AAA HA/LA directors, which themselves would typically be located abreast the forward superstructure, as on a Hipper, were moved back to be abreast the funnel. This did cause complications with the boat arrangement, but it provided overall better arcs for the director (including a largely unobstructed view directly astern) and removed it from the proximity of the 3-meter and 6-meter rangefinders. As a bonus, it freed up some additional arc for the horribly limited 3.7cm SK C/30 twin mounts there. The 3-meter rangefinders abreast the turmmast – located at this level in part due to the limited space below – take up the approximate area where the SL directors would have, and have decent enough arcs for their limited roles (night-time rangefinding and acting as a rangefinder for torpedo firing solutions to name a few). Two additional 7-meter rangefinders can be found integrated in the forward and aft centerline turrets. While rangefinders were located atop the forward pair of broadside turrets in Blucher’s original design – one for each side – the Kriegsmarine focus relies more on engaging on one side for the most part, with a special emphasis on redundancy. For example, in the modernized arrangement, if the forward turret is knocked out of action, then the aft turret can still be used to provide rangefinder data for that engaged side, but could also rotate around to provide for the other side as well. In the original arrangement, had the turret with the larger integrated rangefinder (other turrets had smaller ones, but I am referring here to the larger ones) on one side been knocked out of action, there was no way to continue getting rangefinder data on that side of the ship via the turret-integrated rangefinder on the other side, short of turning the whole ship around to do so.
Unfortunately the shape of the armored housings for these rangefinders is “suboptimal” – a result of compromise to prevent having to tear off and rebuild the turret roofs, which saved quite some time and money at the cost of aesthetics and optimal armor plate angles. Even so, it was a massive step up from the practically non-existent protection found on the original rangefinder housings. Seawater spray was not yet an acknowledged flaw with enough steam to cause the removal of A-turret integrated rangefinders at the time of design, and in the case of Blucher, it is not expected to be much of an issue due to her intended operational area and high forward freeboard.
Smaller optics include the target giver/targeting equipment. These small optics, often confused for simple lookout equipment, are a series of advanced (often stabilized) auxiliary directors which can gather and, with most of them, automatically transmit that gathered data directly to the relevant computer or director to bring them on-target. The main battery target givers (Artillerie-zielgerat, or AZG) are located in the forward and aft conning towers, as well as several being located in the foretop fire control station. Auxiliary versions (Artillerie-zielsaule, or AZS) are located outside of the conning towers, and in the case of Blucher there are a total of four. Two are located on either side of the forward conning tower, with one in each row of targeting equipment. Two more, again one on each side, are located in the aft superstructure. There are two AAA artillery target givers (Zielanweisgerat, or ZAG) located on the foretop, one on each side and aft of the 2cm guns there. They communicate with the SL8 AAA directors and provide preliminary target data as the larger director swings to begin targeting the aircraft. There are a total of six searchlight directors (Scheinwerferrichtgerat, or SRG): one for each searchlight on the broadside. Four are located, two in each row, on either side of the forward conning tower. These control the forward-most searchlight and those located on the searchlight platform attached to the funnel. Two additional SRGs are located, one per side, in the aft superstructure and are for the two searchlights on the mainmast. There are only one pair, one per side, of torpedo target givers (Torpedo-zielapparat, or TZA), and they are also located on either side of the forward conning tower. Finally, there was a Torpedoauswanderungsmesser (TAM), or torpedo deflection calculation device - necessary for accurate torpedo shots. The TAM was located on the centerline in the aft superstructure.

RADAR – The Kriegsmarine had been experimenting with radar afloat most notably since 1938 (though possibly earlier, in 1937, during trials, but this is unconfirmed as far as I am aware) with the Imperial-era torpedo boat G10, but it wasn’t until 1939 that Admiral Graf Spee – just months before the Batte of River Plate and her sinking – became the first ship to test the highly secretive technology operationally. She was fitted with a relatively small 0.8x1.8m “mattress” antenna for a FMG 39 G (gO) – later designated as FuMO 22. By early 1940, many German ships had begun to be fitted with at least one FuMO 22 radar with a 2x4m antenna, typically attached to the face of a newly constructed radar hut atop the foretop rangefinder station. Even at the time of Operation Weserubung, ships like Admiral Hipper, Scharnhorst, and Gneisenau [and KM Blucher] had already been fitted with the new radar, and that number would continue to grow as the war progressed.
Blucher had not originally been drawn with radar, and thus no provisions for it were made during the design phase, but in the interim the technology had proven itself important enough to justify the added delay to have it fitted. Thankfully all the necessary prerequisites were present to allow for easy and quick installation, and Blucher entered service with a singular FMG 39 G (gO) [FuMO 22] with associated radar hut being installed on the foretop 7-meter rangefinder. Experience would unfortunately later show that the early rangefinder housings were not constructed with enough margin for weight beyond the housing and rangefinder itself, and so the added weight of a radar hut and radar gear strained the traverse motors and accelerated wear and tear on the rangefinder(s). This would be rectified on ships such as Prinz Eugen and Bismarck with the introduction of a newly-shaped housing, but for Blucher this issue would remain with her for her entire service.

PRIMARY ARMAMENT – The main armament of Blucher, consisting of six twin 21cm turrets, were still operating just fine even by 1938. Compared with the 20.3cm/60 SK C/34, the reload speeds and traverse speeds were deemed acceptable enough to be left without major overhaul or replacement of relevant equipment (which would have added an unacceptable delay regardless), but the range and most especially the shells available at the time for the 21cm were considered grossly suboptimal. To fix the short range, the Drh. L. C/06 turrets were modified to elevate to 35 degrees, up 5 degrees from the original limit of 30 degrees. Some thought was given to relining the guns to 20.3cm and firing standard Panzersprenggranate L/4,4 projectiles, but instead it was seen as preferable to produce improved 21cm armor-piercing projectiles based on the 20.3cm Psgr. L/4,4 and also utilize these in 21cm guns used by the coastal artillery. The Marinewaffenamt had already designed in secret these new projectiles in the early 1930s, anticipating the possibility that the 21cm turrets would be returned to Blucher at some point, and thus production was already poised to begin during the time Blucher’s modernization was approved and she entered the shipyard. The new projectiles also had a positive effect to the guns’ maximum range, being far more aerodynamic than the simple non-ballistic capped WWI L/2,9 projectile.
One unfortunate aspect that could not be changed was the odd “ammunition highway” that transferred 21cm ammunition from the magazines of the aft broadside turrets to the forward broadside turrets, which did not have magazines of their own. The forward magazines were omitted to provide room for additional boiler rooms - necessary to achieve the 25-knot speeds Blucher was originally capable of. Without magazines beneath these forward turrets, ammunition and charges from the aft turret magazines was lifted to a centerline space between the aft turrets and just below the armored deck (with the armored deck making the roof of this central space). From there, the ammunition and charges were placed on two individual conveyor belts – with a slight gap between them so crew could walk through – and rolled forward to between the forward broadside turrets. The conveyor belts ran in a long, thin, square, centerline space also located directly underneath the armored deck and that made its way in-between the boilers/boiler rooms, which were separated to port and starboard sides by a central longitudinal bulkhead. When viewing a cross section, one would see two large boilers separated by a central bulkhead, but the bulkhead is stopped from reaching the bottom of the armored deck by a small square “box” that appears to be attached to the bottom of the armored deck and “supported” on the bottom by the bulkhead while also being snugly fitted in-between the port and starboard boilers in the small area between their steam drums and exhaust ducting. That “box” is a cross-sectional view of the ammunition highway. Once the ammunition and charges had made their way to the area in-between the forward turrets, they were rotated 90 degrees (with the shells and charges now traveling outboard rather than forward or aft) and were lifted diagonally by two individual hoists to be loaded into the 4-shelf-tall circular carousel immediately below the turret and above the armored deck. 21cm shells would be loaded onto the carousel from one side, and the charges on the other, where they would meet on the other side at the location of the hoists that would lift them up into the turrets to be loaded into the guns. The four levels of the carousel allowed ammunition to be stored near the guns for quick use, but this had the downside of having ordnance above the armored deck and only seriously protected by the belt and barbette armor, which at the Battery Deck level consisted of the 140mm casemate armor and 30mm barbette armor, or just the 180mm provided by the belt armor at the armored deck level as this far down the barbette was no longer armored.
This undesirable, vulnerable, and possibly tenuous broadside turret loading arrangement was kept as a compromise out of an understanding that even the bare minimum length of space required for the replacement machinery system would still be more than the minimum space required to fit magazines between the forward turrets within the citadel, and even the freed-up space ahead of the boilers – which might have theoretically been used – was such valuable real-estate space for vital and necessary auxiliary equipment that in discussions the Marinewaffenamt stood no chance against the arguments of the Marinekonstruktionsamt. And so the arrangement remains, even though MWa correctly pointed out that hits through the horizontal or side armor that landed on the armored deck directly over this very explosive ammunition highway system would send hot shards of shrapnel into it, even if the round did not do so much as perforate the armored deck, and would cause fires which may lead to cookoff and catastrophic explosion. [This happened during Dogger Bank: shrapnel from hits on Blucher caused a fire in the ammunition passageway, causing it to rapidly spread and burn out the forward broadside turrets and their ammunition handling rooms.]
MWa was placated, but far from satisfied, when it was agreed that comprehensive fire suppression and isolation systems, water deluge system, and additional splinter-proof plating, would be added to the entire arrangement or otherwise where possible. If the “ammunition highway” weakness was something (practically) beyond their control, at least its potential danger could be mitigated somewhat.

SECONDARY ARMAMENT – When Blucher was de-armed, serious thought was given to simply plating over her secondary battery and utilizing the interior spaces for alternative purposes. Casemate secondary battery guns were seen as inferior by the Kriegsmarine – especially when compared to turret-mounted guns – and were not kept, even on the old and slow pre-dreadnought battleships where they had been continuously removed over the years. However, the modernization had done much to postpone the same kind of obsolescence that had plagued those pre-dreadnought battleships for decades, and so it was determined that the ship would have her 15cm/45 SK L/45 returned. Rather quickly after, these were swapped for, in part, the new 15cm/48 TK C/36 guns removed from Z8 Bruno Heinemann after her unsatisfactory testing. The remaining barrels came from new production. The older 15cm/45 went on to be used in other applications.
While the secondary battery was acknowledged as preferable to have, some of its magazine space was still allocated to 10.5cm and 2cm ammunition. Not too much 15cm ammunition was lost, as the size of the size of the magazine separating the turbine rooms from the boiler rooms was increased in size to account for the new weaponry.
A firing solution for the 15cm battery could be derived from data provided by just about any rangefinder assigned to provide that data to the secondary guns. This included the 3-meter and even the 4-meter rangefinder used on the SL8 director, though more often it was the 6-meter rangefinder that was used for the task.

AA ARMAMENT – Despite the large increase of superstructure space, very little could be dedicated to anti-aircraft armament. Due to the priority of the main battery and its effectiveness in general (even at the expense of anti-aircraft capabilities) in the pre/early-war period, only a modest AA arrangement – roughly that of a Deutschland-class – was fitted. 4x2 3.7cm SK C/30 guns had to be crammed into less-than-desirable positions around the ship, though the eight single 2cm C/38 guns fared a little better. In the Admiral Hipper-class, the 2cm guns seen abreast the forward superstructure on Blucher would normally be 3.7cm twins, but in this case had to be substituted for 2cm guns so as to reduce the width of the platform and prevent encroaching on the forward arcs of the forward broadside 21cm turrets – an indicator of the relative importance placed on main battery capability compared to that of anti-air during this time. However, as the war dragged on and air power began to play a greater and greater role – just as reliance on the Luftwaffe to provide protection became less and less trusted – things such as main battery arcs or placement of AA in “undesirable” locations (such as under the muzzles of large-caliber guns, or on the extreme bow and stern areas) would fall practically entirely by the wayside.
With the 3.7cm guns unable to be placed “normally”, but still seen as preferable to have 3.7cm guns on the forward end of the ship, covering forward arcs, they were relocated to the Bridge Deck. This is not too unusual of a location for them, as they can be seen in this location on Scharnhorst and Bismarck, but it is not exactly the best position. Worse still is that these guns needed be constantly elevated when not in use to prevent the 6-meter rangefinder from smacking its rangefinder arms into the barrels – such is the tight nature of Blucher’s superstructure.
Fortunately, the foretop and funnel searchlight platform naturally provide 2cm AA positions, meaning that no compromises need to be made for them. The same, however, cannot be said of the aft 3.7cm guns. Although located in good positions with wide firing arcs and acceptable crew working area for the majority of those firing arcs, they are unfortunately also practically a hop, skip, and a jump’s distance away from the muzzles of the aft 10.5cm guns when they are rotated to fire over the aft end of the ship (and consequently also over the 3.7cm guns themselves). This compromise requires the crew to carefully train, deconflicting to prevent possible injury, even though having AA near the muzzle of some large-caliber gun or another, in some way or another, is far from unseen in Kriegsmarine design.
While the location of the forward pair of 10.5cm guns was always obvious, much thought and several revisions were needed for the aft pair. Initial sketches had them abreast the conning tower, in the same location as the previous single 8.8cm guns, but working space was badly cramped and put the muzzles of the 10.5cm guns practically in the faces of sailors operating targeting equipment there when trained directly aft. (This initial arrangement had also forced the use of the smaller Deutschland conning tower, but it was not changed or enlarged when the area was de-congested by moving the 10.5cm mounts further forward, towards midships). Once moved forward, their place was taken by the 3.7cm guns, which was a significantly more sensible arrangement.
The two single 2cm guns aft, just forward of the number 6 turret, were again no problem. Although not as far outboard as is preferable to prevent them being in the line of fire of the aft broadside 21cm turrets, they are still in a perfectly typical and usable location.

TORPEDO ARMAMENT – With practically all other areas had been taken up by equipment and potentially suitable locations restricting or displacing some other piece of equipment, the stern became the clear home of Blucher’s torpedo battery. Shielded types were chosen primarily due to being directly under the muzzles of the aft 21cm turret. To some this is no surprise, as the torpedo tubes for ships like Scharnhorst or Tirpitz have their unshielded torpedo tubes either at or under the muzzle of their 10.5cm or 15cm guns, but it should be made clear that the torpedoes on large capital ships like those of Scharnhorst, Gneisenau, or Tirpitz were not intended for combat, but as a quick and effective means of sinking commerce vessels without exhausting gun ammunition. Thus the torpedo tubes would not typically be manned during combat, and the torpedomen not in any danger of the secondary battery blasting them - one way or another. The shielding was also particularly useful for the sea spray generated at high speed, especially as the stern crouches and possibly causes the stern to become awash (especially during rough seas). They also have the notable benefit of being particularly low-profile, as the firing station typically located atop “normal” Kriegsmarine torpedo tubes would prevent the aft 21cm turret from rotating unimpeded at low elevations.

AIRCRAFT AND CATAPULT – As with most Kriegsmarine ships larger than a destroyer, a catapult and aircraft were practically a necessity. The wide beam and limited height above the deck forced the catapult assembly to be offset to the port side slightly; this offset complicated some things. Most noticeably is the operation of the port 10.5cm mount when the Arado Ar-196 aircraft is mounted on the catapult – though for the most part this will not cause an issue or restriction under most circumstances, the potential for a conflict between the operation of the port 10.5cm and catapult still exists.
Much like German light cruisers or the Deutschland-class, a hangar was not originally envisioned. In fact, that area was instead covered with ships’ boats instead. However, as the design matured, the smaller boats slowly migrated to the open areas around the funnel. With a reduced number of boats now aft of the funnel, a large clear area of deck emerged. Some offshoot designs attempted to cram a single-aircraft hangar into the location, then simply an open-air area for aircraft to be stored, but all ideas ultimately failed and the hangar was abandoned. Eventually, later on down the design process, a page was taken from Kreuzer M, and a recessed hangar with a two-panel vertically-opening hatch roof was made to fit after some effort. The boats on the superstructure ahead of the hangar couldn’t overhang it, and the catapult had to be positioned to be able to rotate out of the way for the same reason.

BOATS – Blucher’s boat complement consists of 9 boats of any measurable size, along with 4 small Dinghy boats. Five of those nine larger boats are motorized, and consist of a singular Admiralsboot, two Verkehrsboote, and two Motorjollen. A pair of Kutter are provided. To make up for the lack of large boats, such as a Motorpinasse, four Dingis are provided. Later into the war, life rafts would begin to be added to further boost the safety net for the ship’s sailors in the event the ship is sunk.
The cranes are the same type used on Prinz Eugen, and have arcs sufficient to reach the larger boats as well as the aircraft and catapult. However, moving the small boats to around the sides and area ahead of the funnel means that the larger crane is now out of reach. To service these smaller boats, two smaller cranes were provided. These were not too uncommon on other Kriegsmarine ships, and served to cover the areas the larger crane could not reach.

CAMOUFLAGE – The camouflage applied to Blucher is based off of 1941 “Baltic Stripes” camouflage used on Prinz Eugen. Being a ship primarily intended for Baltic Sea service, this more unique version of the typical Baltic Stripes camouflage is both particularly alluring and suitable.

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