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The Johnston Model D1918 was a 
A variant was produced without the heat shield jacket and with a bare, unfinned barrel. A muzzle counterweight maintained the normal balance position. A further wooden handgrip was provided ahead of the receiver, as the bare barrel would be too hot to hold, unlike the cooling shroud.
light machine gun
A light machine gun (LMG) is a light-weight machine gun designed to be operated by a single infantryman, with or without an assistant, as an infantry support weapon. LMGs firing cartridges of the same caliber as the other riflemen of the ...
. It is a rare and little-known weapon with scant information available on it. It is best known for its resemblance to the Lewis Gun, having a similar gas-operated action
Gas-operation is a system of operation used to provide energy to operate locked breech, autoloading firearms. In gas-operation, a portion of high-pressure gas from the cartridge being fired is used to power a mechanism to dispose of the spent ...
and a barrel surrounded by a cooling shroud.
The weapon was chambered for the .30-06 round, fed from double drum magazines.Rather than the Lewis pan magazine
A magazine is an ammunition storage and feeding device for a repeating firearm, either integral within the gun (internal/fixed magazine) or externally attached (detachable magazine). The magazine functions by holding several cartridges withi ...
.
The action was gas-operated, with the piston working in a cylinder beneath and integral with the barrel. The Johnston did not use the Lewis's prominent clock spring. Cocking of the piece was unusual, the entire pistol grip sliding forwards to engage the action, then returning backwards to cock it.A similar cocking action was used in the Czech BESA 15mm and was copied for later models of the Besal
The Besal, properly named "Gun, Light, Machine, Faulkner, .303-inch", was a light machine gun of British origin. The weapon was intended as an alternative to the Bren gun as it was lighter, simpler, cheaper and easier to manufacture and therefor ...
emergency production LMG based on the Bren
The Bren gun was a series of light machine guns (LMG) made by Britain in the 1930s and used in various roles until 1992. While best known for its role as the British and Commonwealth forces' primary infantry LMG in World War II, it was also used ...
This was first unlocked by a trigger-like mechanism in a cutout through the grip, behind the firing trigger.
The cooling shroud could be removed without tools by unscrewing the front retaining ring from the barrel by hand. The aluminium cooling fins inside were in two pieces and once the shroud was removed, came loose from the barrel. A cold barrel could be unscrewed for field exchange.Unlike the Bren, where a side handle with extra insulation and leverage was provided to allow a hot barrel to be changed. An integral bipod
A bipod is a V-shaped portable attachment that helps support and steady a device, usually a weapon such as a long gun or a mortar. The term comes from the Latin prefix ''bi-'' and Greek root ''pod'', meaning "two" and "foot" respectively.
Bip ...
was attached to the shroud.
Variants
A variant was produced without the heat shield jacket and with a bare, unfinned barrel. A muzzle counterweight maintained the normal balance position. A further wooden handgrip was provided ahead of the receiver, as the bare barrel would be too hot to hold, unlike the cooling shroud.
Notes
References
Light machine guns Machine guns of the United States {{Mil-hist-stub