If you buy this book hoping it will be about high tech things for GURPS, you will be disappointed. It should be called GURPS guns or something. It is basically the history of firearms, with a few things about explosives and other sundry pieces of information thrown in. It is really quite interesting and well researched. However, it only goes up to modern times, and much of the text is devoted to ancient cannon, guns and so forth.
There are a few peices of information that could be useful to a campaign in here, but mostly it is just background material, and is more geared towards being interesting reading than essential game rules. If you like this kind of GURPS book, you would probably give it more stars than I did.