Much of the uniform and equipment of soldiers during World War One was quite impractical for use inside a tank. In particular, the vision apertures in a tank were so small that it was necessary to keep the eyes very close to them in order to get even a limited vision. Thus, any headdress with a peak was entirely unsuitable.
In May 1918, General Elles and Colonel Fuller were discussing the future of the Tank Corps and its uniform and General Elles tried on a beret of the 70th Chasseurs Alpins who were billeted nearby. A black beret was selected as it would not show oil stains.
No change in uniform was possible during the war, but after a prolonged argument with the War Office, the back beret was approved by King George V on 5 March 1924.
The black beret remained the exclusive headdress of the Royal Tank Corps until its practical value was recognised by others and its use extended to the majority of the Royal Armoured Corps in 1940. On the introduction of the blue beret in 1949, the Royal Tank Regiment reclaimed its right to the exclusive use of the black beret, which may not be worn by any other Regiment or Corps with the exception of the Berkshire and Westminster Dragoons Squadrons of The Royal Yeomanry.