If there's one ugly duckling that turned out to be a swan and the darling of the Air Forces it's the .50-caliber machine gun. It's by no means new. It was developed for ground troops before World War I was over. Of course it was unthinkable for the airplanes of that day.
Fortunately for the United States, however, a great deal of thought, time, effort and money were devoted to its development as airplanes increased in size and strength and utility. And when war came the .50 was a sound, field-tested weapon. Its use, however, was at first limited. Not one of the pursuit planes that got off the ground at Pearl Harbor. for instance, was armed with the .50. They still carried the .30-caliber gun that had been the stand-by of our own and all other air forces, The .30 had great utility. It still has, for certain purposes. Against ground personnel it is probably more effective than the .50 because it fires many more shots per minute and a .30-caliber bullet is all it takes to knock a man out of action. Hence on those types of airplanes designed for ground-strafing troops, a certain number of .30 caliber machine guns are still mounted in the forward firing position.
But for the protection of those planes themselves, for firing against enemy planes and for almost all other purposes, the swing to .50s has been almost universal in American airplanes.
"To quote the sports pages," says a brisk young captain of aircraft ordnance who's served his time on several fronts and has seen both weapons in action, "a good big man can always lick a good little man. And the .50 is to the .30 as Joe Louis is to Henry Armstrong Wham!"
Wham is right. Its armor-piercing projectile will go through twice the thickness of armor plate that the .30 will pierce. What that penetration is remains a military secret for the present, but the Japs and Germans have learned that they have no armor in the air which is protection against a .50-caliber slug. This was a complete surprise to them. It cost them scores of airplanes when they first attacked our Flying Fortresses. It necessitated important redesign of German planes, for instance, and required a complete change in their tactics of attack.
It was an even greater surprise to the Jap. He thought his Zero, with its small caliber machine gun used for aiming and a cannon used for the prospective kill, was better armament than anything we had. But the Zeros began to break up under the blast of our .50s before they could even get within cannon range.
And, fortunately for us, the .50 is almost exclusively an American aircraft development. Even now, when the enemy recognizes its superiority, neither Germany nor Japan have produced an effective counterpart. The British, long devoted to the .30 because it served so valiantly in the Battle of Britain and because it permits a load of more rounds per airplane (and fires more shots per minute) still like the .30 for many purposes. They have taken our .50s, however, and are increasingly arming their planes especially big bombers with this weapon.
Russia has fallen in love with the .50. In Washington they are moving heaven and earth to obtain certain types of our planes with heavy groups of forward-firing .50s. It is understood here that these planes are being used to attack German transport and light armor on the ground. For such purposes our boys in North Africa found the .50 a real devastator. It will rip apart any kind of motor transport except heavily-armored tanks. It not only penetrates ordinary steel but tears it apart in great gashes. Our attack bombers using .50s, and the .50s on Russia's own Stormoviks and other planes have, according to reports here, played real havoc in the rear of Hitler's ever more disorderly retreats this past summer.
Where the .50 earned its real glory, however, is in attack on shipping. Pilots have described the results of a long burst against the sides of a Jap destroyer as "opening it up like a tin can." No topside armor, except on cruisers and battleships, is proof against .50-caliber armor-piercing bullets. They go through standard shields or the side plates of an ordinary ocean-going vessel in a manner to create major structural damage, often putting it out of action or sinking it, And they wipe defensive gunners from the decks.
This has proved particularly effective in the skip-bombing which is rapidly replacing both dive-bombing and torpedo attacks in our war against Jap shipping in the Pacific. When our low-flying planes come in at 300 mph (and over) to loose their bombs against a ship's side from a height of only 50 feet, dodging and weaving, there is only one way a ship can protect itself from the point-blank crash of the missile. It must lay down a screen of shrapnel and high explosive in the attacking plane's path. The planes move too fast and too irregularly for the sharpest gunner to follow an individual plane from the ship's deck and get it with an aimed round.
But the demoralization on a ship's deck produced by a stream of .50-caliber armor-piercing, incendiary, and tracer slugs, from one or more attacking planes dodging in, has proved so great that mass gunnery from the attacked ship proves almost impossible. The effective range of the .50, aimed by the pilot just as he aims his bomb in this point-blank style of attack, is sufficient to drive the men from the guns and let him get to the point where he drops, or rather hurls, his bomb against the ship's side. Once the bomb is away, the pilot is off in a dodging, screaming series of zooms and climbing turns that provides little target for a demoralized gun crew.
The .50 is a heavier installation than the.30 (about three times its weight, or 62 pounds); it can fire only about 800 rounds per minute as against the .30's 1,200 rounds; and its muzzle velocity may be only about five per cent better than the .30, or about 2,810 feet per second. But its maximum range on the ground is 7,200 yards, or over four miles, while the .30's is only 3,400 yards. This difference is accounted for by the weight of the round. A round of .30 caliber ammunition weighs 396 grains, or about 0.9 of an ounce. A round for the .50 weighs 1,800 grains, or slightly over a quarter of a pound.
Of course, ranges in the air are not what they are on the ground. They vary highly among individual gunners. But the fact remains, to the infinite surprise of the German and the Jap, that the .50 has far more range than the .30, in the air as well as on the ground. Hence it means that the enemy, armed only with .30-caliber, machine guns against our .50s, must be within our range of fire much longer than our planes must be in his. He can be destroyed before he can hit us. The .30 may pour more shots in a burst but the .50's bullet is about four times the weight of the .30's, and when it hits, in the words of our ordnance captain:
"Joe Louis! Wham!"
The enemy's tentative answer is the 20-mm cannon. It is an effective weapon. It has range and weight of projectile and it can fire a real explosive shell. Thus battle stories already tell all too frequently of our bomber personnel being wounded by shell fragments. It is against these that our men are successfully testing out personal armor. But the battle stories also tell of our big bombers, in particular, coming home with many holes due to shell fragments, even holes and casualties caused by the explosion of shells within the structures, which cause considerable damage under certain circumstances.
For many purposes our planes are armed and will be further armed with the cannon of as much as or greater power and speed of fire than the 20-mm German Oerlikons and Mausers, for which 800 rounds a minute is claimed. But all of these guns lack the flexibility of the .50-caliber machine gun. They are long-barreled and comparatively difficult to install and handle. The number of rounds they can carry is limited.
If you talk to the boys back from the combat areas, nine times out of 10 and all things considered, they will plump for our own .50 as the most useful and flexible weapon for combat in the air against other airplanes.
It is short-barreled. It may be mounted in the most flexible manner in ball turrets or revolving turrets. At high air speeds, particularly the relative speeds of two planes in combat, which may reach as high as 700 or 800 mph, the stream of slugs from our .50s can be more effectively handled. And most of our gunners believe that when a slug from a .50 does hit it creates as much structural damage and damage to enemy personnel as does any 20-mm cannon shell exploding in or near the structure.
This article was originally published in the January, 1944, issue of Flying magazine, vol 34, no 1, pp 66-67, 156, 158.
The PDF of this article includes a photo of a B-24 top turret, a crew arming P-51 nose guns, and a comparison photo of the .30 and .50 aerial guns and cartridges.
Photos credited to US Army Air Forces, Colt's Patent Fire Arms Manufacturing Company.