From the summer of 1942 until the end of 1943, Ernest Hemingway spent much of his time patrolling the Gulf Stream and the waters off Cuba’s north shore in his fishing boat, Pilar. He was looking for German submarines. These patrols were sanctioned and managed by the US Navy and were a small but useful part of anti-submarine warfare at a time when U boat attacks against merchant shipping in the Gulf and the Caribbean were taking horrific tolls. While almost no attention has been paid to these patrols, other than casual mention in biographies, they were a useful military contribution as well as a central event (to Hemingway) around which important historical, literary, and biographical themes revolve.