As part of the British Army's reaction to the potential invasion threat, it was required to establish rapid reaction forces. These organisations were highly mechanised and lightly armed.
They only existed between May and December 1940. The Motor Machine Gun Brigades were established from Cavalry and Armoured Units. It was likely that these units did not have sufficient armoured vehicles to equip them as they were intended.
The formations were the 1st MMG Bde, 2nd MMG Bde, and 3rd MMG Bde.