Let's say gravity drives exist. This is a device that can power a spaceship by creating an artificial gravity well some distance in front of the spaceship that the spaceship perpetually falls into, much like the carrot on a stick approach:
This device requires a ton of energy to power (no violating conservation of energy), but is helpful because it allows space ships to accelerate substantially faster than 1G without squashing their occupants.
Here are the specs that I have so far:
- The drive is quite big; let's say the size of an Olympic swimming pool.
- The drive allows accelerating a 500m long ship at 10G (and has parameters that are appropriate for projection strength and projection distance to make that possible without imposing crazy sheer forces on the ship), but can't do much more than that on current energy production.
- The drive doesn't work in strong gravity gradients, such as if it's sitting on a planet's surface.
- The drive has some mechanism by which it doesn't violate conservation of momentum (like ejecting propellant opposite the attraction is necessary to maintain the gravity source).
What is a "good" military use/exploit of this technology (besides the obvious use of getting your spaceships to a place faster)? One key aspect of this technology is that it would take a lot of energy to power, so to be a "good" application, it needs to be something that can't be achieved with simpler technology on a similar energy footprint.
For example, can you use it to chuck asteroids at planets? Yes, but as far as I can tell, not for less energy than if you just pushed the asteroids with space ships with conventional chemical engines. So, unless I'm missing something in my analysis, I wouldn't classify this as a "good" use because it's not something that the gravity drive itself enables.
Example 2: can you put your gravity well in the middle of another spaceship to crumple it? Sure, but to count as a "good" use, this has to be more effective than hitting them with a payload from a mass-driver (and I'm not sure why it would be).