The U.S.S. Avalon was constructed in 2422. It's design was heavily influenced by the U.S.S. Dauntless - a science vessel, discovered by the crew of the U.S.S. Voyager, which was actually alien in origin. The Dauntless featured Quantum Slipstream Drive technology, which was groundbreaking at the time, but ultimately this ship was created using Particle Synthesis to fool and trap the crew of the Voyager. In 2410, the blueprints for the original alien starship were closely examined and StarfleetEngineering Corps were able to re-create and, eventually, improve upon this vessel.
Previous attempts to utilize Slipstream technology on testbed designs, (such as the Vesta Class), had been met with a limited degree of success. Slipstream velocities could only be maintained for a limited time. In order to maintain the slipstream, the phase variance of the quantum field had to be constantly adjusted, or the slipstream would collapse, violently throwing the ship back into normal space. Re-initializing the Slipstream Drive would also take an extended period of time.
It would eventually transpire that most of these problems originated from attempting to essentially 'graft' or adapt the Slipstream Drive onto pre-existing warp drive designs, since all the newer designs utilizing the drive were equipped with both types of FTL propulsion. Ships would generally use warp for standard FTL travel and reserve their Slipstream drives for short 'jumps' over vast distances.
The Avalon class would mark Starfleet's Engineering Corps first attempt to create a 'pure' Quantum Slipstream vessel, designed from the ground up to channel energy from the engines through the vessel's main deflector. In order to make this process as efficient as possible, the nacelles have been built directly into the secondary hull, essentially making them into a single unit. The sleek, bullet shaped hull also allows the ship to withstand the enormous quantum stresses placed upon the hull during Slipstream transit. These major design modifications now enable the Avalon to go further and faster than any starship before it, as the drive can finally and reliably be engaged for extended periods.
At 450 metres long, the Avalon is roughly twice the size of the original Dauntless design. The ship is also equipped with new specialized 'weapons blisters' that utilize replicator technology to reconfigure the weapon emitters to almost any type. As long as the schematics of any type of weapon have been entered into the ship's database, (and the energy matrices are compatible) then the ship can create the emitter to suit requirements. This gives the Avalon the ability to fire a wide variety of beam weapons, pulse energy weapons, plasma based weapons and torpedo types.
And we all know that having a dual warp system has it's tactical advantage, seeing as how the Dauntless couldn't reenter Slipstream after reaching Borg space in time to avoid assimilation.