A Sourcebook of Weapons & Equipment Through the Ages.
The second book in the series of GURPS supplements detailing historical technology, High-Tech covers GURPS tech levels 4 to 7 (Renaissance to Modern).
One of the first books released for GURPS Third Edition, it, along with GURPS Magic, were essentially extensions of the main rule book.
High-Tech concentrates on weapons and related combat equipment. There are sections on transport and communication, but they are fairly brief.