Andrew Cook's younger brother, Dallas Harry Cook was born on 19 May 1921. He enlisted in the U.S. Marine Corps on 14 August 1940. After service at Quantico, Guantanamo Bay and Puerto Rico, he served in the field from 14 February 1942. He was promoted to sergeant on 21 May 1942 and was killed in action in the Raid on Makin Island on 18 August 1942. He was posthumously awarded the Navy Cross for his actions during the raid.