Private Brennie was a member of the 3rd Anti-Aircraft Artillery (Automatic Weapons) Battalion, 3rd Infantry Division. On 5 December 1950, he was crossing a bridge in an armored vehicle when the bridge was blown up by the enemy.

Brennie was awarded the Purple Heart, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal, the Korean Presidential Unit Citation and the Republic of Korea War Service Medal.