1/350 US Navy 20mm Oerlikon MK 2 / MK 4 (45º elevation, Square Shield) x12

1/350 Scale US Navy 20mm Oerlikon MK 2 / MK 4 (45º elevation, Square Shield) x12. These are highly detailed parts modelled using the John Lambert plans and reference photographs to create the most accurate and detailed 20mm Oerlikon MK 2 / MK 4 available anywhere.

• 12x Mounts (these Mounts carry the Squared off Shield without the Notches)
  
• Highly detailed and accurate parts, modelled from the John Lambert plans and photographic reference
• Hex nuts, accurate Rivet placement, 60 Round Ammo Cartridge, Sights (including Cross-Hairs) and Operators Rests
  
• Barrels elevated at 45º elevation and Depressed (firing).
  

HISTORICAL DATA
Widely used by many nations, this 20mm automatic weapon originally designed by the Swiss firm of Oerlikon was probably produced in higher numbers than any other AA weapon of World War II.

In 1937 the British Admiralty initiated tests to find a weapon suitable for arming merchant ships and minor warships against close range air attacks. They rejected the Oerlikon Model 1934, but in 1938 the Admiralty informed Oerlikon that if they could raise the muzzle velocity and demonstrate that the weapon could be used and maintained by non-specialist personnel, such as fishermen and merchant seamen, then it would be acceptable. Oerlikon made the necessary changes and the first prototypes of the new design were delivered late in 1939. These were immediately accepted into service as the 20 mm Mark I and Britain placed large orders with Oerlikon and obtained a manufacturing license. However, only a few additional guns were delivered prior to the German occupation of France, which cut off the supply route. This is basically why so few British ships had Oerlikon guns during the early part of the war, with the official USN BuOrd history stating that the Royal Navy had only 100 Oerlikons at sea in November 1940.

Shortly before France fell, the British took advantage of their manufacturing license with Oerlikon to obtain a set of production drawings. These were brought back from Switzerland by Stewart Mitchell, who had previously been Inspector of Naval Ordnance Contracts at the Oerlikon factory in Zurich. Mitchell, together with the famous ordnance expert Charles Goodeve and with Cmdr. S.W. Roskill (then working in the Admiralty Staff Division and later the famous Capt. Roskill, author of "The War at Sea") set up a factory at Ruislip to produce Oerlikon guns. "Considerable difficulties" with equipment and labor had to be overcome before deliveries of the British version of this gun, designated as the 20 mm Mark II, began in the fall of 1941. In November 1941, the battleship HMS Duke of York was commissioned with six of these weapons, which I believe to have been the first warship to carry British-produced Oerlikon guns "as completed.”

It is not specifically known how many guns were built by Britain and the Dominion nations, but the Mounting Appropriation Lists of September 1945 show about 55,000 guns in service in the British and Commonwealth navies. This total probably includes weapons built in the USA that were provided as a part of Lend-Lease or installed on those ships refitted in US shipyards. Some British Auxiliary ships still carried these weapons as late as 2006.

The Mark 1 was the original design by Oerlikon. A small number of this version were built in the USA as prototypes. The USA Mark 2 and the British Mark II were the first production versions manufactured in those countries. The differences from the Mark 1 were mainly in the arrangements of the buffer springs, although the USA Mark 2 also had cooling ribs and two locking slots. The USA Mark 3 was similar to the Mark 2 but had fewer cooling ribs and only one locking slot. The later USA Mark 4 was the most common version built in the USA and had a single, heavier buffer spring. This version was built to slightly different tolerances as it was redesigned using English measurement units rather than the metric units used on previous Marks. The Mark 4 Mod 4 had a fluted chamber which allowed easier ejection of the spent cartridge cases. The Mark 1 could be fired in single-shot mode, while all of the others could only be fired in automatic mode. All guns used a monobloc barrel and a horizontal sliding breech block mechanism.

These guns are open-breech, air-cooled and use a gas blow-back recoil system. This weapon has some unusual features not found in other automatic guns. When fired, the case pushes the breech back against the force of the barrel springs. The barrel does not recoil, the breechblock is never locked against the breech and is actually moving forward when the gun fires. This weapon lacks a counter-recoil brake, as the force of the counter-recoil is checked by the explosion of the next round of ammunition.

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