Following the outbreak of the Second World War, Andrew was appointed commander of the 22nd Battalion, which he led during the Battles of Greece and Crete as well as the early part of the North African Campaign. For a short period in late 1941 he commanded an infantry brigade of the 2nd New Zealand Division, and was awarded the Distinguished Service Order for his leadership. He returned to New Zealand in 1942 and commanded the Wellington Fortress Area for the remainder of the war. He retired from the military in 1952 with the rank of brigadier, and died in 1969 aged 71.