From the introduction:
Sourcebook 1: Grand Fleet Hero is a supplement for the Traveller Hero version of the Traveller RPG. The nominal ‘game universe date’ is around 1111, in the Late Golden Age, but virtually everything contained in this book is valid in 993. At that time, of course, the Solomani Rim War is raging and the Fourth and Fifth Frontier Wars have not yet been fought.
This book contains some rules and stats specific to Traveller Hero, but general information can be used with any rules set. It does not attempt to deal with the minutiae of any given region, fleet or situation. Instead it presents an overview of the Imperial Navy; what it does and how.