From the back of the book:
The universe is hostile. The small privately owned starships travelling between the stars are vulnerable to many dangers, from faulty drives to hijackers and from piracy to open warefare. Good maintenance, security and the constant vigilance of small gunships protect against the first three threats. However, if war was to break out the only hope for safety would be provided by the Imperial Navy and its mighty Fighting Ships.
THe ships within this book form the frontline of defense against hostile governments. Without these vessels the galaxy would be a much more dangerous place and few would dare travel across the vast emptiness of space.
Fighting Ships introduces a whole new range of ships to Traveller, to be explored. used or fought. The spacelanes have just got a little more exciting...