At the same time, in the US, a half-inch high velocity round was being developed for use against aircraft. It would be used with the Browning-designed .50 calibre machine gun. This round was based on current US .30-06 calibre infantry ammunition. When word of the German anti-tank shell spread, there was some debate as to whether it should be copied and used as a base for the new machine gun cartridge. However, after some analysis the German ammunition was ruled out, as its performance was inferior to the modified Springfield .30-06 round and was semi-rimmed, making it difficult to feed into an automatic weapon. The Browning M2 .50 cal machine gun would go on to function as an anti-armour machine gun.