On June 28, the above expansion was authorised, and the personnel for new units was assembled at the Training Centre at Wool. A month later, however, the call for manpower became so urgent that the expansion of the Heavy Branch had to be suspended. It was on the 28th of this month that the Heavy Branch became known as the Tank Corps.
During the following months, August and September, the question of the Tank Corps expansion was held in abeyance. On October 6 it was once again revived, and a revised establishment for the contemplated expansion to eighteen battalions was submitted. The outstanding feature of these establishments was the abolition of Battalion Workshops and the substitution of Brigade Workshops in their place. This resulted in a considerable economy of man-power, and was rendered possible by the higher training of the tank crews; each tank with its crew thus tended to become a self-contained unit.
On November 27 these establishments received official approval, and exactly one week later, on December 4, arising out of the overwhelming success gained by tanks at the battle of Cambrai (November 20), two new organisations were put forward, the first known as the Lower, and the second as the Higher Establishments. The Lower Establishments were eventually decided upon, and they consisted in a revised edition of the former establishments with various additions, which the experiences gained at the battle of Cambrai had shown to be necessary. These establishments, though made out, were never approved, and the German offensive in March 1918 found the Tank Corps still organised on the lines agreed upon in October.
In April, on account of the pressing needs for infantry reinforcements, the Tank Corps expansion was temporarily suspended, two of the three remaining battalions in England being reduced to cadre units, and the third converted into an Armoured Car Battalion. In July and August the astonishing successes gained by tanks on various sectors of the Western Front once again brought forward the need of increasing the British tank battalions, and the suspension was removed, the two remaining battalions of the expansion of October 1917 proceeding to France in September 1918.