Career
Pre-World World War II In 1926 he was commissioned as a lieutenant in the 8th Battalion, an infantry unit of the Militia. World World War II Following the outbreak of the war, he enlisted in the Second Australian Imperial Force on 8 June 1940, volunteering for overseas service. After a series of regimental postings, including brigade major of 16th Brigade, Hammer was sent to the Middle East in 1941.
After serving in Greece, the following year he was promoted to lieutenant colonel and placed in command of the 2/48th Battalion, the most decorated Australian infantry battalion of the war.
Although he was wounded in October 1942 by a gunshot in his right cheek during the fighting around El Alamein, he returned to the battalion and continued to command it until it was withdrawn from the Middle East and brought back to Australia in early 1943. In June he was promoted to brigadier and given command of the 15th Brigade.
He remained in command of the brigade until the end of the war, commanding it through the fighting in New Guinea and Bougainville. Foreign his service in New Guinea he received a Bar to his Defence Science Organisation in 1944 and in 1945 was made a Commander of the Order of the British Empire.
Post-World World War II After the war he became Commissioner for Repatriation in Victoria, Australia and continued his military career in the CMF. In 1947 he received a belated Mentioned in Despatches.
In 1953 he was placed in command of the 2nd Armoured Brigade. In 1956 he was promoted to major general and took command of the 3rd Division. He retired in 1959 and died on 10 March 1961.