The scene is set in HMS Narwhal, cruising at 300 feet under a 12 foot thick Arctic ice cap. Gavin and his crew have been on patrol for a month, tracking Russian nuclear submarines and reporting on the feasibility of patrolling under the ice for nuclear submarines. First-hand experience of an emergency on the ice above reveals how the Arctic is a bleak, awesomely beautiful but unforgiving place.
Further reading:
Land Bridge Theory: http://ows.edb.utexas.edu/site/hight-kreitman/land-bridge-theory
