The Me 262A-1a / U1 is a modification of the world's first mass produced jet fighter, the German Me 262 ‘Schwalbe’. The armament of the A-1 sub-serie, being four 30mm MK.108 auto cannons, had a number of drawbacks, such as cycle failures and complex heavy shell ballistics. For these reasons, engineers experimented with different variations as to the weaponry, including a reinforced cannon battery. As such, the Me.262A-1a/U1 modification was created as part of this program. German engineers managed to fit 6 autocannons in the nose: 2x20mm MG.151/20, 2x30mm stock version MK.108, and 2x30mm MK.103 guns. For the latter, they developed shells with a higher initial speed, and the guns themselves had a longer barrel length than the MK.108, as well as an effective muzzle brake - all to improve the ballistics of the heavy shells. They built a prototype (according to other sources, there were three units), but the project was not entered into mass production. However, one example was flown by one of the most effective jet aces of World War II, Heinz Bär, who flew it at the end of April 1945, and with it, even shot down several Thunderbolts in the skies over Germany.