had a barrel change, the headspace and timing had to be manually set. Improper adjustment could damage the weapon and cause serious injury to the user. Fixed headspace and timing reduces risk, and the carrying handle allows the barrel to be switched in seconds. In June 2011, the Army began conversion of M2HB machine guns to M2A1s. The M2A1 was named one of the greatest Army inventions of 2011. As of November 30, 2012, 8,300 built or converted M2A1s had been fielded by the U.S. Army; the program will upgrade the Army's entire M2 inventory of more than 54,000 guns. The U.S. Marine Corps plans to upgrade all of their ground-mounted M2s to M2A1 standard from 2016 to 2018. The first phase of conversions was completed in March 2017, with 3,600 M2A1s planned to be fielded by the Marines in total. The Israel Defense Forces adopted the M2-HQCB (the commercial version of the M2A1) in 2012 as a replacement to the M2HB. FN Browning M.1939 One derivative of the M2 Browning is the Mitrailleuse d´Avion Browning - F.N. Calibre 13,2 mm, more commonly known as the FN Browning M.1939. The FN Browning M.1939 was a heavily modified M2 Browning for aircraft use designed by FN Herstal for export. Their aim was to make a light, reliable heavy machine gun with the same damage output as a 20 mm autocannon. To achieve this they raised the firing rate to 1080 rpm and gave it a more powerful cartridge in form of the 13.2×99mm Hotchkiss. This cartridge was a popular Eurasian analog of .50 BMG developed independently in 1920s with a 13.2 mm bullet (.52 in) and more propellant. A new projectile was designed for this gun. It was of a high explosive type and was designed to take down a small aircraft with a single hit. Tests showed that it was very effective against both cloth and aluminum skinned aircraft. Due to the aforementioned improvements, the gun received interest from numerous nations when it entered the export market in 1939. Due to the start of World War 2 and the invasion of Belgium it was exported to only Romania and Sweden. Sweden was able to buy the majority of the weapons along with the blueprints to produce the weapon on their own without paying for a license. In Sweden, the weapon received the designation Automatkanon m/39, short Akan m/39, meaning Autocannon