High Guard looks at virtually every aspect of the concept of a space navy that you can imagine, from an expanded character generation system for characters who have served (or even still are serving) in the navy to ship construction, space battles and naval adventures. If your Traveller game uses the 'Official Traveller Universe' the Imperial Navy will be a watchful presence any time the party ventures into the black, while if you have designed your own universe there's likely to be some form of military presence in space and this work will help you to create it. As well as the Imperial Navy, sub-sectors and even individual worlds may maintain their own navies to keep the space lanes open and defend against hostile incursions.
After an introduction that sets the scene, we move on to the first section, Creating a Navy Character. Based on the character creation processes in the core rulebook, this adds depth and variety to the Navy career allowing characters to attend Naval Academy before embarking on a career as a naval officer and to specialise in different branches of the service: Crewman, Engineering, Pilot, Gunnery, Command, Support, Small Craft Pilot, High Command, Naval Intelligence and Naval Research. All these are gone through in extensive detail. Characters can also choose to serve in the Imperial, subsector or planetary navies... and there's even a list of the medals that they might be awarded during their careers!
Next a section on Spacecraft Options begins the part of the book devoted to spaceship design. There's lots here to keep the would-be ship designer happy, covering everything from capital ships to small craft.
Once you have created all those vessels, the next section, Expanded Space Combat, enables you to test them against one another as it looks at every possible aspect of combat in the depths of interstellar space whether it is a battle between capital ships or a fast and furious brawl between single-pilot fighters.
Slightly confusingly, we then get back to ship construction with a section on Small Craft, which also gives plenty of examples of ready-made ones, and then on to a series of specimen capital ships - useful if you want one but do not have the time or inclination to go through the design process. Here, some of the deckplans are not well rendered, being rather cramped and blurry, making them difficult to read and only capable of giving an overview of the vessel concerned rather than the level of detail you will need if using them in a game.
Finally, there's a section on Naval Adventures. This looks at running a campaign where the characters are on active service, rather than independent adventurers with naval backgrounds. Several general ideas are presented and there's a random system for generating missions to use (or to gain inspiration from) as you design adventures.
Whether or not the party is still in the navy (or indeed has ever served), this book has its uses both in the ship design and combat sections and for providing a wealth of detail about the navy which will, of course, be at least there in the background even if it rarely features largely in your plots.