Wading in to murking waters here. In NEM Riker was given command of a ship we never see. The USS Titan. In 2005 there was a contest for the USS TItan pocket books. To design what the ship would look like. Now this is the books so it's canoncity status is shakey.
The Star Trek Online Wiki gives the best description of the ship because it is playable in the game. Also check Memory Beta since Luna class ships are unoffical.
After the Dominion War, Starfleet commissioned the Luna class ships. Which from the sources above classify them as science and reconnaissance vessels.
Remember this is apocryphal since this class of ship was never shown on screen.