This was my first introduction to Tom Clancy, and remains my favorite book. The opening chapter is Clancy at his best: terrorists attack and destroy an oil refinery in the Soviet Union. This forces the Soviets to essentially launch an offensive against the rest of the world to secure their energy future.
The weapons systems, military strategy, and various points of view on both sides of the conflict kept me riveted the whole way through this massive volume. If you liked The Hunt for Red October, this one's just as good.