The 1st Dragoon Guards was a Cavalry Regiment that would have had an MG Section as part of its Regimental Headquarters. These weapons would have been brigaded when the Machine Gun Corps was formed in 1915. The guns, and crews, would have been formed into a Machine Gun Squadron.
This remained until the formation of Divisional Machine Gun Battalions in 1936 where guns were brigaded once again. As Cavalry regiments were largely mechanised, their use would have been as per the Royal Armoured Corps.