Tom Clancy is the maestro in the genre of "military fiction" and this book is considered one of its best.

A Russian nuclear missile submarine (carrying over 150 warheads, enough to annihilate half of the USA) with a new extra-silent is led by a commander and a group of officers who want to defect to the USA. The Russian fleet chases it, the Americans raise their own fleet to answer the provocation and brilliant intelligence plot to take it over.

This book is interesting in two aspects. One is the pure military story - chases between submarines, battle-groups of carriers, and so on. All sounds very realistic (except for a too-machoistic behavior of the commanders/sailors). The other is the interesting intelligence/politics games on the two sides. It's a complicated setting, where each side has spies on the other side, double agents, sleek ambassadors and so on.

The action is enthralling, especially the quick jumps from one place to another in times of intense activity.

This book has some downsides, like loose ends and inconsistencies (it feels as if Clancy planned the "caterpillar" to be a real feat, but then changed his mind), but overall it's pretty good, and certainly very interesting to read.