Where eagles dare / Alistair MacLean.

Enhanced descriptions from Syndetics:

Forbidding peaks, resourceful commandos, beautiful spies, nonstop action, and neck-snapping plot twists make this the classic adventure thriller--the kind of page-turner that readers actually will find impossible to put down. A team of British Special Forces commandos parachutes into the high peaks of the Austrian Alps with the mission of stealing into an invulnerable alpine castle--accessible only by aerial gondola--the headquarters of Nazi intelligence. Supposedly sent in to rescue one of their own, their real mission turns out to be a lot more complicated--and the tension climbs as team members start to die off, one by one. Written by Alistair Maclean, author of the Guns of Navarone, this is the novel that set the pace for the modern action thriller (the film version, with Richard Burton and Clint Eastwood, also helped), and it still packs twice the punch of most contemporary best-selling thrillers. What's more, the cast of spooks, turncoats, and commandos who drive this story are more relevant than ever in our new era of special forces, black ops, and unpredictable alliances.