That makes sense- in space combat, chemical explosives aren't much use except as bursting charges for shrapnel warheads, since the kinetic energy of any mass traveling >3 km/s is indeed greater than the potential energy stored up in any chemical explosive. A dumb rock lobbed at the speeds typical of interplanetary flight doesn'tany explosives. But, a shrapnel warhead is a great idea- you get a spread of projectiles each able to do considerable damage, and covering a larger area so you don't have to aim so terribly precisely, just place the shot where the target will fly through the expanding shrapnel cloud. It is funny to think that the weapons we use on the final frontier might not be so terribly removed in principles from our earliest- all that separates a thrown rock from an orbital strike is the speed and energies involved.Gravity being the weakest force, and one which we humans haven't much idea how to practically manipulate, I can't comment on gravitational warheads.But in the fictional physics of WW1 spaceships I suppose the gravity-altering physics behind spaceship drives could open up the way to weapons able to stretch a battleship apart like it had wandered too close to a rogue black hole...