The M2 Machine Gun, Browning .50 Caliber Machine Gun, is a heavy machine gun designed toward the end of World War II by John Browning. It is very similar in design to Browning's earlier M1919 Browning machine gun, which was chambered for the .30-06 cartridge. The M2 uses the much larger and much more powerful .50 BMG cartridge, which was developed alongside and takes its name from the gun itself (BMG standing for Browning Machine Gun).
A Soviet assault on a combined American and German Emergency Militia position, between Frankenberg and Arnsberg, was broken when an American .50-caliber machine gun began firing. It had been a desperate fight with even a MG-42 not stopping the charging infantry but the .50-caliber bullets began to throw hit men every which way. That was too much for the Russians who broke and ran.
The .50 caliber M2's were issued to the US Army and the US Cavalry during their war with the Race. It's .50 caliber slugs were more than capable of punching through the body armor the Race's infantry wore.