High Quality Content by WIKIPEDIA articles! The No. 73 grenade, also known as the Thermos or Woolworth bomb, was a British anti-tank grenade used during the Second World War. It got its nickname from the resemblance to a Thermos flask. With the end of the Battle of France and the evacuation of the British Expeditionary Force from the port of Dunkirk between 26 May and 4 June 1940, a German invasion of Great Britain seemed likely. However, the British Army was not well-equipped to defend the country in such an event; in the weeks after the Dunkirk evacuation it could only field twenty-seven divisions.