The official version in the Series was, that every ship needs to be refittet to launch quantum-torpedos. So every "old" class still uses photon-torpedos, even when the q-t?s became common to the defiant and the sovereign.
But i am not really sure, a quantum-launcher can?t launch photons. Maybe they are downwards compatible. For exmaple, a normal projectile gun can fire smaller bullets, with an adapter.
That would explain, why a quantum-equipped ship can fire photons, but an old "photon-ship" can?t fire quantums.
Armament 4 phaser cannons, at least 3 phaser emitters, at least 4 forward torpedo (photon and quantum torpedo) launchers, at least 2 aft torpedo launchers, BUT it is just easier to have 2 quantums up front and 2 photons in back.
Last edited by asardetemplari; 08-31-2012 at 06:21 AM.