The "Thetis"-class cruisers were 142 meters long, 15,2 meters wide and with a draft of 5,2 meters (5,7 fully loaded). Their standard displacement was 5200 tons, maximum - 5780 tons. They resembled the traditional French Navy armored cruisers of "Ernest Renan" type.
They were armed with 138-mm/55 cannons, modele 1910, the same guns that were used as secondaries on French Navy dreadnoughts and superdreadnoughts. The intial design suggested the use of older, 45-caliber long guns, but eventually ships were re-designed to use newer guns.
Eight main guns were placed in four dual turrets, one on bow, one on stern, and two at the center, in echelon arrangement. All turrets were electrically-powered; the max elevation was 30 degrees, which gave guns the maximum range of 18000 meters (by using the heavy SAP shell).
The secondary armament was composed of eight quick-firing 47-mm Hotchkiss guns, placed on weather decks and in hull ports. Also the cruisers were armed with four 450-mm underwater torpedo tubes, five torpedoes per each.
The armored belt have a maximum thickness of 80 mm at upper edge and reduced to 40 mm at lower edge. At the ends, the belt thinned to 40 mm at upper edge and 20 mm at lower edge. The belt was 2,5 meters high, of which almost a meter was below the waterline. Horizontal protection was composed of 30 mm armored deck with 45 mm slopes. Turrets were protected by 100 mm plates, their barbettes were 65 mm. Conning tower was armored with 80 mm plates.
The powerplant differ from ship to ship. All have mixed, oil-coal boilers of different designs. "Thetis" have combined powerplant with two Rato turbines and VTE at central shaft; other cruisers have all-turbine arrangement, but their turbines were from different builders. They generally have around 25000 ihp, and speed around 26,2-27 knots. The coal & oil supply allowed 4500 nm of 10-knot steaming.