These are gyro-stabilised but unguided rockets fitted with an advanced microfusion warhead.
The warhead only has a simple dumb impact fuse, which limits its combat usefulness, but it can't be spoofed, flared or decoyed by advanced ECM weapons. It just flies in a straight line.
Rockets are difficult to hit a moving ship with, but the hammer packs a much greater punch than a gnat rocket, making it ideal for use against large targets.