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The Bofors gun that revolutionised air defences

The Bofors gun that revolutionised air defences

8 min read

Few products developed in Sweden have received so much publicity and have been of such historical significance as the Bofors 40 mm gun. It has been portrayed as one of the weapons that came to determine the outcome of the Second World War.

Morning dawned with a grey shimmer across the English Channel. A sight was unfolding on the steel-blue water that eye-witnesses would never forget. The sea had turned into an armada. More than 5,000 ships loomed on the horizon carrying 150,000 soldiers, the largest seaborne force that had ever been mobilised. It was 6 June 1944, D-day, and the Allies would land on the occupied beaches of France with the aim of finally crushing Nazism.

“Our progress from the beach was slow and at one point we were tangled up with the glider-borne reinforcements landing across the St Aubin Darquenay-Benouville Road. On arriving at Le Port just north of Benouville we were attacked from the church tower by a sniper.”

The air shook with deafening noise. Wave after wave of bombers and fighters were blasting German positions. Battleships fired projectiles that roared over the pale beaches. The soldiers waded ashore through seaside resorts, summer homes and old Normandy villages.

Some 80 anti-aircraft battalions brought with them thousands of Swedish-designed light anti-aircraft guns, the Bofors 40 mm gun. The weapon was one of the most successful of its kind and was praised for its speed and precision. The gun could be used against moving targets in the air and against ground-based targets and was available in several versions – the most popular of which was on a mobile gun carriage for the army.

James Holder-Vale joined a troop from the 92nd Light Anti-Aircraft Regiment in the Royal Artillery. The men had six self-propelled Bofors guns and were tasked with protecting the bridges around Benouville from air attack.

An officer gave the order to turn the Bofors guns on the church tower and with a considerable volley from the 40 mm gun, a large hole was blasted in the wall. Miraculously the German sniper survived and was taken prisoner.

“For five days the Germans made many concentrated attacks to destroy the bridges and cut off our left flank, but each attack was met with accurate fire from the Bofors and during that time the Luftwaffe lost 17 confirmed attackers. The Germans couldn’t sustain such losses and gave up low level bombing”
-recalls Holder-Vale

The bridges were to be defended at any price. The German aircraft attacked over the next few days. Daredevil pilots circled level with the treetops and were met with powerful fire from the Bofors guns, which were famed for their precision.

The ‘Bofors Gun’ gained an almost mythical status during the Second World War and was used by almost all the fighting forces. It was used with particular success in the defence of London at the time of the German air raids during the Blitz. Bombing of the British capital was a nightly occurrence for almost two months in 1940.

The Bofors gun that revolutionised air defences

Revolutionary design

The Bofors gun was an example of the highly specialised and for its time revolutionary designs which the engineers at Bofors successfully produced during the inter-war period of the 1920s and 1930s.

World War I had shown that there were a number of new challenges that the countries of the world needed to adapt to. Perhaps the most serious of these was the threat from the air, from air forces. At the start of the First World War the major powers only had a few hundred aircraft each. But development was rapid. By the end of the war the countries had equipped their air forces and had tens of thousands of planes. The use of aircraft by air forces led in turn to the need to develop effective air defences, which applied both to the army and navy.

Bofors observed the new leap in technology and was already delivering anti-aircraft guns to the Swedish Navy in the final stages of World War I. But they were not efficient - their ballistic performance was inadequate and the ammunition was unsuitable. 

The Bofors management knew that their traditional strong competitive advantages, high-quality steel and first-rate powder were not sufficient to keep up with rapid developments. In the 1920s the company therefore began some design and development work to completely overhaul their range of products.

A driving force It required team work, but one person stood out as a driving force: the chief engineer, Victor Hammar, head of the design engineering department from 1921 onwards. He went on to become acclaimed both in Sweden and abroad for his inventions and weapons technologies. There were no insoluble problems as far as Hammar was concerned. He knew that you sometimes had to take winding detours to find the right answers. His right-hand man was the engineer Emanuel Jansson.

On 25 November 1928 Bofors was commissioned by the Royal Swedish Naval Materiel Administration to develop a special new anti-aircraft weapon: a 40 mm gun. The prototype was a British gun which had been tested in Sweden for some time. Most of the design work took place in 1929, a year that marked the end of the ‘Roaring 20s’ with the Wall Street Crash being the most talked-about event.

Bofors first unveiled a semi-automatic gun which could fire 250 rounds in five minutes. But Hammar and his colleagues were not content with that success. They wanted to produce a really efficient fully-automatic gun. Development continued over the next few years and many firing tests and modifications took place.

After five years’ work the first fully-automatic gun was ready to go into operation in 1934. The 40 mm Bofors gun was the result of around 30,000 hours of work at the drawing board. The gun came out at a time when the whole world was aware of the major threat from the air and it was big news. It is probably one of the most acclaimed products ever in the history of weapons.

Word soon spread and many foreign delegations succeeded one another on study trips to Bofors. There was also ‘Mr Bofors’ – Bertil Boström – a naval officer employed at the company, who was a knowledgeable specialist who skilfully marketed Bofors products around the world.

The big breakthorugh

The big breakthrough came at firing tests in Belgium in 1935 against a British competitor. It was found that the Bofors gun could be moved more than twice as quickly as the competitor’s gun and that it scored three times as many hits when firing on aerial targets. The Belgian officers were amazed.

The demonstrations in Belgium took place in the presence of representatives from the French War Ministry. It soon resulted in an order from the French Army, which was quite remarkable. Traditionally, France bought no guns from abroad.

The Bofors gun that revolutionised air defences
Few Swedish-developed products have been so rewritten and gained as much historical significance as the Bofors 40 mm canon. It has been portrayed as one of the weapons that came to determine the end of World War II. Bofors AB archives.

The Bofors gun was shown to surpass everything that the international defence equipment industry had so far achieved. It was fast, accurate and stable, it could be moved on roads at various speeds and could even traverse rough ground. The time for transport to firing was shorter than for any other artillery piece and the ammunition was superior in terms of its effectiveness and reliability.

The orders now started arriving at a rate that Bofors had never known before. Deliveries of guns and ammunition were combined with licensing agreements in a total of eleven countries. The largest foreign orders came from Argentina, Belgium, the United Kingdom and the Netherlands. A total of around 1,500 guns were ordered in the period 1934-1939.

Major success in the USA 

The Bofors gun was particularly widely used in the US armed forces and the name of Bofors came to be equated with high quality. The USA had for some time been investing in the development of a 37 mm gun, but US officers became curious about the Bofors 40 mm gun after the UK and France had purchased it. Initial contacts between Bofors and the USA took place in 1938. The business discussions were complicated by the outbreak of World War II in 1939, but in July 1940 a gun was ordered through the US Embassy in Stockholm. It was delivered along with test ammunition in the utmost secrecy by truck from Bofors to Petsamo in northern Finland. From there it was taken on board a ship that was evacuating US citizens from Scandinavia.

In the USA the Bofors gun became an integral part of the US air defences and production of the gun under licence began, mainly at the Chrysler Corporation in Detroit. Chrysler is said to have manufactured around 60,000 guns and more than 120,000 gun barrels in all. However, Bofors was not satisfied with the payment they received for subcontracting and it was only well into the 1950s that a final financial agreement was reached.

The Bofors gun that revolutionised air defences
Boforskanonen got a particularly big place in the US defense and the name Bofors became equivalent to high quality. A license production took place at Chrysler, a total of about 60,000 pieces and more than 120,000 electric pipes were made. The image from 1938. Bofors AB's archive.

On the other side of the Atlantic the Bofors became part of the collective consciousness. The Bofors gun was even made into a toy and was probably found in many Christmas presents during the war years. The expression ‘Quite Bofors’ also became widespread and came to mean something like ‘great’ or ‘first-rate’.

The new 40 mm gun became important for Bofors at many levels. Not only did the gun make the company and its name known throughout the world, it also had a major strategic and defence significance in many countries. The 40 mm Bofors gun also formed the basic design for lighter automatic guns and led to the company developing an entire product family of efficient guns ranging in calibre from 20 to 57 mm.

Soon after the Second World War it became clear that the Bofors 40 mm gun would not be suitable for use against the new jet-powered aircraft. But the ‘faithful old servant’ still survived in modified form in many countries’ armies and even today there are still some left in the Swedish Navy.