Yet photon torpedoes are always shown leaving their launchers at a snail's pace, compared with the concept of them reaching another ship hundreds of thousands of kilometers away in no time flat, let alone them doing warp. Independent acceleration after an essentially "swim-out" launch is what the visuals would be consistent with.
Perhaps torpedoes attain their speed after launch by firing a separate booster stage? Basically, you shove the warhead into the launch tube, automation adds the booster like one would add the bag of cordite into a cannon after the shell, and both are spat out in a brilliant ball of light that makes it impossible for us to see the booster stage.
A regular torp can then maneuver and, if necessary, slow down using those four engine nozzles astern. K'Ehleyr's gutted probe cannot...