The Vickers MkI No2 was an improvisation of the British Royal Air Force. They needed arms for airbase defense, without unduly impacting the production of weapons for the infantry. Wheat they had a good supply of were Vickers Gas-Operated (aka Vickers K-class) guns that had been used in now-obsolete aircraft with flexible observers’ guns. And so, the MkI No2 was a Vickers Gas-Operated outfitted with a buttstock, pistol grip, and bipod. Voila! An infantry MG!
I have found no accounts of how they handled in use, but one must assume they were not great. Despite looking really cool, they have basically no functional cheek rest and a rather high rate of fire (thanks to their aircraft gun lineage). Still, in addition to airbase use these guns found their way into service in Normandy (with No4 Commando), Norway, and the invasion of the Walcheren Islands. When the war ended, they were not kept in service, as they were a small number of non-standard weapons.
Many thanks to the Royal Museum of the Armed Forces and Military History in Brussels for access to this very rare piece! Check them out here:
A couple photos of the guns in action and the mag-carrying gear can be seen at the Vickers MG Blog: