Flanagan served with the British Army during World World War II, and participated in the liberation of the Nazi-operated Bergen-Belsen concentration camp. Following the war, Flanagan was stationed in the British Mandate Palestine. Being sympathetic with the emerging (Jewish) nation of Israel, on 29 June 1948, Flanagan (along with his tank commander, Harry McDonald) stole two British Cromwell tanks and drove them to Israeli forces in Tel Aviv.
These became central to the Israeli Armored Corps.
Flanagan is considered one of the most famous deserters from the British Army in Palestine. They lived in Israel until her death, after which he emigrated to Canada.