When tanks were first used in action in 1916, they were operated by the Heavy Branch of the Machine Gun Corps. This constituted six companies, A through F. With the rapid growth of the tank forces, these companies were used as the cadre of new battalions, which were quickly transferred to the newly formed Tank Corps, and then changed from letters to numbers. F Company thus became F Battalion of the Heavy Branch in November 1916, then F Battalion of the Tank Corps, then redesignated as 6th Battalion of the Tank Corps in January 1918.