The Vickers “K” Class gun – also known as the Vickers Gas Operated – was the gun the Vickers company thought would replace the heavy water-cooled Vickers and allow them to remain primary machine gun supplier to the British army. The design actually came from the French designer Berthier, who has expected it to be adopted by the French Army – when it wasn’t he sold his rights and patents to the Vickers company. Much to their surprise, in British light machine gun trials of the 1930s it was beaten by the Czech ZB-26! So the Vickers company pivoted, and decided to up the gun’s rate of fire and offer it to the air force as an observer’s gun to replace the Lewis. In this it was successful (and it would also be adopted as an infantry gun by the Indian Army).
The Vickers K is probably best known for its use by the SAS/LRDG raiders in North Africa. For them, the high rate of fire was ideal, and the guns were available from disabled aircraft (and not easily converted to an infantry configuration).