Antiaircraft guns (also known as “flak guns”) have been the been the bane of combat aviators’ existence since the advent of air combat itself during World War I.

For example, during World War II, the German FLAK 36 88mm multi-purpose gun made life a living hell for Allied bomber crews in the skies over Western Europe, such as the U.S. Army Air Force's 8th Air Force B-17 Flying Fortresses participating in “Black Thursday,”  the October 14, 1943, bombing raid against the ball-bearing factories in Schweinfurt. (Incidentally, “FLAK” was a shortened form of Flugabwehrkanone, meaning “aircraft defense cannon”, and this was how the word entered the military lexicon in the first place.)

Fast-forward to the Cold War, and you had Soviet designs such as the 23mm ZSU-23-4 "Shilka" and ZU-23, along with the 14.5mm ZPU-4 that made their presence felt during the Korean War, Vietnam War, and the 1991 Persian Gulf War.

But of all the world’s great anti-aircraft guns, nothing can compare to two particular guns that were coincidentally made in Western European countries and whose names begin with “Sw,” namely Sweden’s 40mm Bofors and Switzerland’s 20mm Oerlikon guns.

40mm Bofors Initial History and Specifications

The inspiration for the 40mm Bofors gun traces back to the 1920s when the Swedish Navy expressed a desire for a more capable replacement for their Vickers Pom-Pom anti-aircraft guns. The Swedish Navy brass handed this request over to AB Bofors (founded in 1646 and headquartered in Karlskoga, Sweden; now part of British arms manufacturer BAE Systems) who entered into a contract in 1928 and had their product ready for the production range by 1933.

The gun operated on a gravity-assisted feeding mechanism that was manually loaded with 4-round clips. Specifications and vital status include:

-Crew: four

-Barrel Length: 7 feet 5 inches (2.25 meters)

-Gun Carriage Weight: 1,151 pounds (522 kilograms)

-Projectile Weight: 2 pounds (0.9 kilograms)

-Muzzle Velocity: 2,800-2,900 feet per second (850-880 meters per second)

-Maximum Range (theoretical): 23,600 feet (7,010 meters)

-Max Effective Range (practical): 12,500 feet (3,810 meters)

-Rate of Fire: 120 rounds per minute (cyclic/theoretical); 90 rpm (practical)

The gun ended up being used by the armed forces of a whopping eighty-four different countries at one time or another!

20mm Oerlikon Initial History and Specifications

The ordnance for this weapon actually dates back to 1918, when German arms engineer Reinhold Becker came up with a 20x80mm round that fired using primer ignition blowback in a very large machine gun to fire 300 rounds per minute. Fast-forward to 1934 and the Swiss-based company Oerlikon Contraves (Oerlikon for the eponymous town the factory called home and contra-aves being Latin for “against birds”; now known as Rheinmetall Air Defence AG) resurrected Becker’s design and upsized it to more effectively engage the modern monoplane fighters of the 1930s.

Production began in 1937. Specifications and vital status include:

-Crew: four

-Barrel Length: 55 inches (1,400 millimeters)

-Gun Carriage Weight: 150 pounds (68.04 kilograms)

-Projectile Weight: 4.3 ounces (123 grams)

-Muzzle Velocity: 2,700 feet per second (820 meters per second)

-Maximum Range (theoretical): 14,400 feet (4,389 meters)

-Max Effective Range (practical): 4.921 feet (1,500 meters,)

-Rate of Fire: 4,80 rpm (cyclic/theoretical); 320 rpm (practical)

The U.S. Navy adopted the gun in November 1940. Multiple countries obtained manufacturing rights, thus resulting in the weapon being utilized by both Allied and Axis forces during the war.

Operational History/Combat Performance

The Bofors and the Oerlikon proved to be a terrific tandem for nearly the entire gamut of Allied naval vessels during World War II, spanning the size spectrum of itty-bitty destroyer escorts (DEs) and slender submarines all the way up to the big boy battleships and aircraft carriers. For example, at the end of the scale, the U.S. Navy Gato-class subs had one Bofors and Oerlikon each to back up the 5-inch (127mm) main deck gun, and DEs like the valiant USS Samuel B. Roberts (DE-413) wielded two twin-mount Bofors and ten single-mount Oerlikons. At the opposite end of the scale, the Essex-class “flattops” packed anywhere from thirty-two to seventy-two of the 40mm guns and fifty-five to seventy-six of the 20 “mike-mikes” … and then there were the Iowa-class battlewagons which absolutely bristled with no less than eighty of the 40mm guns and forty-nine of the 20s.

Of course, the Bofors wasn’t just mounted on warships, but on a variety of ground-based weapons platforms, both stationary gun mounts and mobile (tanks, trucks, etc.).

So, just how effective was the 40mm gun? According to Jesse Beckett in a January 24, 2022, article for War History Online titled “The Bofors 40MM Revolutionized Anti-Aircraft Combat”:

“The British held the gun in extremely high regard and put a massive emphasis on its production during the war. In fact, Commonwealth factories produced over 19,000 Bofors 40 mm guns … During D-Day, Bofors guns were vital in protecting newly captured areas, with crews from the Light Anti-Aircraft Regiment, Royal Artillery shooting down 17 enemy aircraft over the Orne River in France … The weapon also holds the title of being the first ground-based anti-aircraft weapon to shoot down a jet aircraft – in this case, it was a German Me 262.”

As for the Oerlikon, its kill record was certainly nothing to sneeze at either; Daniel Garas of Naval History and Heritage Command cites an anti-aircraft summary published on October 8, 1945, that credits the 20mm cannon with 617.5 enemy aircraft shot down between 1941 and 1945.

The 40mm Bofors continues to make a literal and figurative impact today, ironically now with the proverbial script being flipped, i.e., being used from an airplane against targets down below rather than vice versa, as part of the arsenal of the AC-130 Spectre gunship. Meanwhile, the 20mm Oerlikon still arms some naval units, nominally as a last-recourse anti-air weapon (somewhat akin to the Phalanx CIWS, albeit with nowhere near the impressive buzzsaw-like rate of fire of the Phalanx), but mainly used for firing warning shots or incapacitating small vessels.

About the Author: Christian D. Orr

Christian D. Orr is a former Air Force Security Forces officer, Federal law enforcement officer, and private military contractor (with assignments worked in Iraq, the United Arab Emirates, Kosovo, Japan, Germany, and the Pentagon). Chris holds a B.A. in International Relations from the University of Southern California (USC) and an M.A. in Intelligence Studies (concentration in Terrorism Studies) from American Military University (AMU). He has also been published in The Daily Torch, The Journal of Intelligence and Cyber Security, and Simple Flying. Last but not least, he is a Companion of the Order of the Naval Order of the United States (NOUS). If you’d like to pick his brain further, you can ofttimes find him at the Old Virginia Tobacco Company (OVTC) lounge in Manassas, Virginia, partaking of fine stogies and good quality human camaraderie.

 Image: Shutterstock.