Ships of the class
The Challenger-class USS Buran was a "kitbashed" design study and filming model built by Ed Miarecki and Michael Okuda that was barely glimpsed among the wreckage of the "graveyard" scene in TNG: "The Best of Both Worlds, Part II".  It was made from parts of AMT/Ertl USS Enterprise-D model kits, no. 6619, specifically the saucer section and warp nacelles, as well as from parts of a submarine model kit. Okuda recalled on the model, "I don't recall what Ed's original version of the Buran was, but I added the submarine parts and glued on the engines, although it looks like Ed assembled the engines. I thought it was a clever idea, but it ended up looking like a lollipop. Maybe Ed's version was a single nacelle, and I added the second. I don't remember. (...) I think one of the engine mounts was a submarine tower, but I wouldn't swear that both were. I'm pretty sure both engines were fairly stock Ertl large Galaxy nacelles that Ed had made. The actual amount of modelmaking time that Rick S. and I had was minimal, so we would tend to have stuck with stuff that Ed did for us." 
In the Star Trek: The Next Generation Annual story "Thin Ice" published by DC Comics, the USS Marco Polo (β) was stated to be a Challenger-class starship. This design appeared as a variant of the Constellation-class design, with the lower nacelles replaced by a secondary hull. 
According to issue #114 of the Star Trek: The Official Starships Collection, the Challenger-class had an approximate length of 390 meters, an approximate crew of 300, and a top speed of warp 9.6. This class was equipped with phasers and photon torpedos.