Pretty hard to direct. If you've set up a close-orbiting neutron star binary and you're in a military frame of mind, one thing you could do is accelerate missi

Pretty hard to direct. If you've set up a close-orbiting neutron star binary and you're in a military frame of mind, one thing you could do is accelerate missiles to a good fraction of lightspeed. (Same principle as the gravity assists used by planetary probes like Voyager.) The tides would limit the practical size of the missile, though I haven't tried to compute this limit. (I don't consider this comment to be aiding the interstellar enemy, it's too obvious.)