Towards the end of the First World War heavy bombers began to get small amounts of armour to protect the vital components of the aircraft such as engines. When the Germans did this, they logically began to think about how to defeat the armour. They turned to a weapon that had been patented in 1914 by Reinhold Becker. This weapon was an extremely light weight cannon in 20mm. It was fed by a top loading magazine. Interestingly the ammunition that was used were solid shot, not explosive rounds. This was due to the Saint Petersburg Declaration of 1868. This had forbidden the use of explosives within projectiles of under 400 grams (some sources say 450g). It was the French, and their designer B Hotchkiss who calculated the minimum size of projectile that would be needed to carry a legal amount of explosive, which was 37mm. Which explains why there were so many 37mm weapons in the first half of the 20th century.
The Becker gun was fitted to several German aircraft during the war and was even planned to be fitted to armoured vehicles. Just after the gun was introduced the German aircraft carrying the gun was shot down and discovered by the Allies. At the time they had no ammunition for it though.
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| A Becker 20mm mounted aboard what looks suspiciously like a Hansa-Brandenburg W.12 |
After the war there was a realisation that the St Petersburg treaty needed revision. A summit of lawyers was put in place, and modifications were agreed, stating that light cannon could be used against aircraft. This treaty was never signed, but it became an informal agreement. It should be noted that the British had been using incendiary projectiles against Zeppelins during the war, but would not allow the ammunition to go overseas in case the pilot was shot down and found to be carrying such ammunition in his plane.
A condition of the Treaty of Versailles was that Germany had to demilitarize, this of course included the Becker works, and a ban on the production of guns was in place. Becker had a connection to a small automotive company in Switzerland, called Seebach Maschinenbau Aktien Gesellschaft, better known by its initials SEMAG. The move to Zürich was backed by the German authorities, and thus the Becker gun entered production as the SEMAG aircraft gun. Later a modified form was produced called the SEMAG infantry gun in 1921. In this version the cartridges and barrel were both longer, giving a higher muzzle velocity. It appears there were several sub variants of both SEMAG weapons. In 1923 a heavier 25mm version was built and tested, however the company collapsed before any further work could be done.
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| SEMAG 20mm Aircraft gun |
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| SEMAG 20mm infantry gun |
Another German clandestinely controlled company then stepped forwards, Oerlikon. They took over the SEMAG-Becker cannon's development. There's a hazy period in this weapons history around this time. It seems that over the next decade the SEMAG style guns were widely sold, by Oerlikon, although some of the designs are slowly being refined. They appeared in
The Chaco War, Spanish Civil War and The Abyssinian Invasion. They were used mostly in the role of light anti-aircraft gun. The British brought some for testing as an anti-tank weapon. They had a carriage consisting of a pair of light unpowered tracks, so that the weapon could be pulled by a Carden-Lloyd carrier, along with a gun limber. When limbered the gun was folded flat against its carriage, but to fire it, the weapon was erected while still on the carriage. Some sources say this was around 1935, which seems unlikely, as by 1935 the British were looking at the 2-pounder, equally the uniforms give the appearance of an earlier time frame.
As the Second World War neared suddenly the demand for both aircraft and AA cannon increased, and the later variants of the Oerlikon were widely sold around the world and was likely used by just about every nation except the Soviets. Often the cannon would be on both sides of the battle. Consider the Allies against the Japanese. The Oerlikon armed both sides fighters, equally both sides would be using the same gun on their ships as an AA weapon. In the US alone over 120,000 Oerlikon's were manufactured, and in US service they shot down some 617 aircraft during the war. Banks of 20mm's lined larger US ships ready to protect them against Japanese Kamikaze attacks. The guns simplicity (it had just five parts that could break, and all were on the bolt) and the ability to quickly change a barrel in just 30 seconds meant it was well liked. Indeed, the gun much updated is still in service today.
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| SEMAG's/Oerlikon's in service during the Chinese civil war/Japanese invasions. |
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| A rank of Oerlikon's on the USS Hornet |
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