On 11 May 1943, the 17th Infantry Regiment of the US 7th Infantry Division invaded the Aleutian island of Attu which had been occupied by the Japanese a year earlier. The rocky terrain, fanatical resistance, and arctic weather conditions caused thousands of casualties on both sides. On 29 May 1943, the 1200 remaining Japanese defenders banzai charged their attackers and broke through the American lines. The Japanese attack was only stopped after vicious hand to hand combat with the regiment’s rear echelon troops. The Japanese secretly withdrew from the nearby island of Kiska shortly thereafter. The Battle of Attu was the only battle fought on US territory in North America during the Second World War.