I seem to remember that the Defiant was pretty tough. If memory serves me correctly, that little ship was capable of inflicting major damage from its guns. But what made the pulse canons so strong? And why didn't a larger ship like a Galaxy have the same kind of weaponry? Was it a new technology and therefore would be installed on future starships?

If the enemy ship manages to adapt the Defiant can fall back on its trusty pulsed phasers and qunatum torpedos. 
