There's quite a bit about about sailing in the book, so if you like that sort of thing, you'll get plenty of it. To me it started to seem like padding after a while, but Curtis/Pournelle makes up for it at the end with some really nice chase/pursuit sequences in an experimental plane.
This was a sort of middling book for me. It's okay, and Crane's all right as a character, but there's nothing to make it stand out. It's just as well the Pournelle gave up on spy fiction and turned his hand to SF. He's done a lot better work in that field. I'd recommend this only as a curiosity, and cheap copies can be found easily on the Internet.