From the back cover:
The second rules supplement for the Traveller roleplaying game, High Guard allows you to command the most powerful space fleets ever assembled.
Dedicated to Naval characters, whether actively serving on a frontline warship or semi-retired on a rusting tramp freighter, High Guard expands the possibilities of space combat and ship design.
Naval characters will benefit from new career options and choices made during creation will see them prepared for the worst the galaxy can throw at them.
Budding naval architects can create massive capital ships and swift, deadly fighters with a new and hghly evolved startship construction system. With a wealth of choices for weapons emplacements and other additions, no captain will want to venture into space without this important manual at his side.