Grandfather of the LSW concept. The Browning Automatic Rifle was a heavy automatic rifle with a bipod. It could deliver automatic fire and retain mobility in the squad advance to contact (known at the time as "walking fire"). In short supply when the Americans entered WWI in 1917, it became very popular with the troops when finally issued in significant numbers. Firing the long-cartridge .30 Cal round, it stayed in service with the US Army throughout WWII. The only drawback was its short 20 round magazine.
The M1918 BAR pictured here is a RARE .303 variant.
Sweden as usual, Had thier own variant of the BAR along with a belt-fed variant.
Bonnie & Clyde used the 'Barrow Scattergun', Which was basically a sawn-off BAR.