[Llarry]

Military aircraft guns -- a short survey...

Aircraft gun armament began in World War I, initially with a single rifle-caliber 7.62mm or 0.30 inch diameter barrel machine gun and soon progressing to a pair of fixed forward-firing machine guns. That seemed to be the standard for a number of years. Larger aircraft with multiple crew members often had flexible machine guns for defense.

My cursory research indicates it was the 1930s when a larger caliber machine gun was first used; Boeing fighters of the 1930s used either twin .30s or one .30 and one .50. By the beginning of World War II, 20mm cannon were appearing but the armament was mixed -- twin 7-8mm and one or two 20mm. Into the war years, U.S. fighter armament stabilized at six .50 (12.7mm) machine guns, although the Republic P-47 upped the ante with eight guns. Later in the war, some U.S. fighters used 20mm cannon armament. The Northrop P-61 night fighter had four 20mm plus four .50 cal in a turret; most Grumman F6F-5N night fighters had twin 20mm plus four .50 cal machine guns. And some Marine Corps and Navy F4U Corsairs substituted four 20mm cannon for the normal six .50s. Flexible U.S. armament generally continued to be .50 cal. Late in the war, the Boeing B-29 tail gun installation was twin .50s plus a 20mm cannon.

Virtually all these U.S. guns were of older origin; the 20mm was derived from Hispano-Suiza origins and the .50 caliber machine gun was invented by John Browning in World War I, albeit in early water-cooled form.

By the late 1940s, the venerable .50 was still the gun of choice for flexible armament in bomber turrets and six .50s was the standard for Air Force fighters. The Navy was transitioning to four 20mm cannon.

The Korean war provided a wake-up call: The MiG-15 had two 23mm cannon and a giant 37mm bruiser (admittedly with a low rate of fire.) The Air Force converted a number of their North American F-86 Sabres from six .50s to four 20mm under a classified program and put them into action. Future USAF fighters would be 20mm-armed.

At about the same time, the flexible .50 cal machine gun was being replaced in some applications by the larger 20mm. The Air Force's B-36 heavy bomber had up to six twin 20mm gun positiions, although the planes went through a weight reduction program that removed most guns in later years.

Back in 1946, General Electric had begun design of a new gun with an extremely high rate of fire, using the principle of rotating barrels. Development took some years and the first guns, designated the 20mm M61 and nicknamed the Vulcan, were fitted to the Lockheed F-104C Starfighter. The M61 Vulcan quickly became the weapon of choice for new Air Force applications, adopted in the Republic F-105 and in the tail of the B-58 Hustler (and later the B-52H Stratofortress.) The Navy was more skeptical of the utility of aircraft gun armament and their1958 fighter competition winner, the F4H-1 (F-4) Phantom II did not have gun armament at all. The F-4 could carry a gun pod if desired but accuracy was not very good.

Then Vietnam happened; Navy fighter crews flying the F-4 were frustrated by a lack of air-to-air missile reliability. Other Navy fighter squadrons with the F-8 Crusader each had four of the older M3 20mm cannon and scored a number of gun kills. The F-8 pilots declared themselves the "Last of the Gunfighters" to the annoyance of the Phantom fliers. By the end of Vietnam the Navy had replaced the pair of conventional 20mm cannon in the Vought A-7 attack aircraft with an M61 Vulcan. The Navy had finally seen the light.
//To be continued//