Fifty caliber

Virtually every American fighter and bomber is armed with the versatile, extremely flexible Browning M2 .50-cal machine gun. Almost doomed in the early twenties by economy-minded legislators and some earth-bound commanders, the possibilities of this outstanding gun were foreseen by a few ground technicians in search of a powerful offensive weapon. The once-standard .30-cal gun has all but disappeared from American warplanes, and no tactical aircraft of any consequence in the Army now mounts this weapon. Appearing on training aircraft, the .30-cal replaces its bigger brother due to the cheaper cost of the ammunition and more elastic handling of the gun.

Initial development of the .50-cal goes back as far as World War I where it was used successfully by ground troops, but remained too heavy to permit any feasible usage by aircraft. The great utility of the smaller, lighter .30-cal has enabled the weapon to be chosen for many tasks where it was better suited than the .50-cal Against ground personnel, it is more effective than the heavier gun as its rate of fire is some 300 rounds per minute faster, and a .30-cal slug is all that is necessary to knock a man out of action.

Hence on most foreign ground-strafing aircraft, the .30-cal is preferred when the mission demands attacks against enemy personnel. But on American warplanes the greater firepower, striking force and longer range of the fifty make it a preferred weapon. Its armor piercing projectiles will pierce twice the armor plate that the thirty is capable of penetrating. The heavier .50-cal gun is capable of hurling two and a half times more destruction than the smaller thirty.

Many a fragile Nipponese Zero has disintegrated or flamed fiercely under withering blasts of the chattering fifty before getting within the short range of their low muzzle velocity cannon. Also capable of matching the 1,000 yard range of the German aircraft cannon, the fifty has dissolved Nazi tactics of sitting out of range of a bomber's defensive weapons and methodically firing well-aimed explosive shells while at a safe perch. Even the British, long devoted to their effective, but too light .303 Browning, have begun to change over to the heavier fifty wherever the medium between the .303 and a cannon is necessary, notably in their bomber armament.

Russia quickly realized the potentialities of the fifty, and in Washington are striving to obtain more of certain types of our planes with heavy groups of forward firing fifties. Mounting either four or six forward firing .50-cal. guns and a 37-mm cannon, Soviet Airacobras have proven best suited when employed to attack German transport and light armor on the ground. Russia has purchased over 4,000 of these cocky little fighters. Notably successful were the victories scored by the fighters and also by Douglas Bostons. British reports indicate that as many as twelve .50-cal guns are mounted in the nose of the Bostons, situated at a downward angle to achieve better strafing tactics. Another of the Russian favorites is the North American Mitchell, which literally swarms with .50-cal guns firing from all angles similar to the larger Boeing Fortress. The Red air force reports that the fifty not only penetrates ¾-inch steel, but rips great gashes in enemy vehicles of all types except the most heavily armored tanks. Our attack bombers use fifties almost exclusively, while the deadly Red Stormovik has a battery of 12.7-mm UB machine guns, equivalent to the Browning M2, supporting its twin 32-mm anti-tank cannon.

Particularly effective against enemy shipping, the fifty has a demoralizing effect upon gun crews. It will slice through standard shields or side plates of an ordinary vessel with sufficient force to create major structural damage. Our pilots who have made strafing attacks upon enemy destroyers describe the effect of a long burst of .50-cal fire against the gun positions' topside armor and sides of the ship as opening them up like tin cans. Japanese destroyers have gone down under the concentrated fire of several Naval fighter planes — by the destructive force of .50-cal guns alone!

There are various combinations of mounts for the f1exible .50-cal. On fighters, as many as four are mounted in the wing of an aircraft, as in the case of the Republic Thunderbolt. The well-known Lockheed Lightning has the vicious firepower of four fifties plus a heavier 20-mm cannon concentrated in the nose and firing freely. The Bell Airacobra's 37-mm cannon is well augmented by synchronized and free firing fifties. North American's latest Mitchell hurls lead from fourteen .50-cal guns, ten of which may fire forward at one time, while the bristling array of firepower is very capably supported by a heavy 75-mm nose cannon. Two waist and two tail guns complete the armament of the world's most heavily armed warplane.

The fifty has appeared in dorsal turrets, manual and power-operated tail turrets, flexible waist positions, flexible dorsal and ventral positions, nose chin turrets, remote control turrets, ventral ball power turrets, giving our medium and heavy bombers the best defensive firepower in the world. In free-mounted, manually operated bomber positions, wild and violent bucking of the guns is prevented by the excellent flexible gun mount perfected by the ordnance department of Bell Aircraft. Our latest dive-bombers mount at least four free-firing .50-cal guns firing forward for strafing attacks, plus one or two more dorsal defensive weapons.

A heavier installation than the .30-cal, the .50-cal gun weighs about 64 lbs, or about three times the weight of the 21¼ lb thirty. A highly efficient automatic weapon, it is built to precision standards and produced with three types of barrels for various applications. The water-cooled anti-aircraft model weighs 121.5 lbs, the widely used Tank and Field model is in the 80-lb class. Working parts, however, which automatically perform the numerous mechanical applications while the gun is firing, are the same in all three models. Maximum firing rate is about 800-900 rounds per minute, and muzzle velocity is about 5% greater than that of the .30-cal, or about 2,810 feet per second. Maximum range of the weapon on the ground is 7,200 yards, or over four miles, while the maximum effective range of the thirty is 3,400 yards. The difference is accounted for by the weights of each round of ammunition. A round (one shell) of .30-cal ammunition weighs .9 of an ounce, while the .50-cal slug is slightly over a quarter of a pound. Range in the air is cut considerably with both guns due to the necessity of minimizing the recoil, but varies greatly with individual gunners. Range of the wing and fuselage mounted fifties on fighters is 500 yards, while for the flexible and turret mounted guns of the bombers it reaches 1,000 yards.

Care of the Gun

The cleaning and oiling of machine guns is tedious work; however, its importance cannot be overstressed as the success of any gunnery mission is directly dependent on the manner in which machine guns are serviced. Armorers should clearly understand that the gun cannot be properly cleaned unless all foreign matter has been removed from the gun ports, all salts and metal foulings deposited during firing have been washed away, and all traces of moisture have been removed from the metal surfaces prior to applying lubricating or preserving oil, as the case may be.

Guns which are covered with light or heavy rust-preventive compound (cosmoline) must be cleaned thoroughly to remove every trace of the rust preventive. The firing pin and firing pin extension must always be removed from the bolt and the firing pin spring removed from the extension before cleaning the gun. Care must be taken that parts removed from one gun are not reassembled in another weapon. This will insure maximum performance since the parts were already broken in to a certain extent when they were test fired at the manufacturing point. All gun parts with the exception of the oil buffer and back plate assemblies should be placed in a vat of boiling soda ash solution and remain there for thirty minutes. The cosmoline which gathers on the surface of the water must be skimmed off at short intervals.

After all the parts are cleaned off as above, they should be swirled in dry cleaning solvent to remove any remaining traces of rust-preventive compound, then wiped completely with a clean, lintless cloth or blown dry with dry compressed air and then oiled with either the lubricating or preserving oil as necessary. The oil buffer and back plate assemblies are cleaned separately by hand with dry cleaning solvent to prevent damage to the oil buffer packing and back plate fiber disks.

All guns must be cleaned immediately after firing. The gun must be disassembled by removing the components from the receiver and cover. Great care must be exercised in cleaning the barrel bore. A clean cloth saturated with rifle bore cleaner must be pushed back and forth through the barrel several times, and repeated with clean saturated patches two or three times, then rinsed with clean water and dried thoroughly. Bores should be inspected for metal fouling visible as slight smears of metal left by the passage of the bullet through the bore, and if present, the bore must be cleaned with hot soapy water or soda ash solution. The muzzle should be inserted in the container of hot solution with the rod and cleaning patch inserted from the breech and pumped six or seven times. Then the barrel must be removed, rinsed and dried, inspected and oiled accordingly.

Oil is removed by means of dry cleaning solvent, all dirt and foreign matter from the gun parts by means of a suitable brush, steel wool, crocus cloth or scraper. Repeat the washing in the dry cleaning solvent, then remove the solvent with a clean lintless cloth.

The front end of the barrel extension and bolt as well as cover group parts and firing pin must be cleaned with a rifle bore cleaner applied with a lintless cloth, except the rear portions of the bolt and barrel extensions. They do not need cleaning with the rifle bore cleaner since the bore cleaner is intended to remove salts deposited in firing and the salts do not reach these parts. Gun parts are best oiled by wiping with a clean grit-free lintless cloth which has been saturated in oil and wrung dry. The fixed gun is designed for installation on, near or below the engine, preferably buried within the cowling, or, when set in the wings, flush with the blast tubes sometimes protruding from the leading edge of the wing. This type has an operating slide which connects with the bolt by means of the bolt stud. The operating slide is provided for retraction of the breech mechanism and for use in loading, unloading and the reduction of firing stoppages.

Battle reports seem to indicate heavier guns being carried aloft. The newer uses of planes as ground-cooperation equipment call for heavier air-borne artillery such as the 75-mm cannon mounted on the North American B-25G and B-25H Mitchells. But even here the cannon is bolstered by batteries of .50-cal guns providing necessary fire cover for the comparatively slow-firing cannon. Other weapons reign supreme in their particular class, but the fifty still ranks as the best gun in existence today for aerial slugging and is easily adaptable for almost every conceivable use as an aerial weapon.

This article was originally published in the July, 1944, issue of Air Tech, vol 5, no 1, pp 41-42, 68.
The PDF of this article includes detail photos of the installation of .50s on A-20, P-38 and B-26 aircraft.
Photos credited to Douglas Aircraft Co, Harold W Kulick, Lockheed Aircraft Corp, USAAF.