Our Firepower Developments

Reprinted from Air Force, the official AAF service journal.

by Col Frank C Wolfe

Modern firepower has transformed the aircraft from a mere plane with guns to a package of guns with wings.

Combat experience has necessitated re-arming our fighting planes. The trend is toward new and increased firepower and our accomplishments are making American fighting planes the world's most formidably-armed aircraft. Our recent firepower development, as much of it as we can discuss at this time, includes:

The firepower problem is not new. Aircraft armament dates far back to 1909, at College Park, MD, when the Wright brothers were training our first military aviators — among them today's commanding general of the Army Air Forces, Gen Henry H Arnold. There the first machine gun, carried in the lap of a passenger, was fired at a ground target from a flying machine. It was there also that crudely fashioned bombs were taken aloft and dropped on targets.

Subsequent steps in converting the airplane into an effective military weapon were made during the first World War when Germans and Allies introduced new methods of fitting their planes with machine guns and bombs. As early as 1915, German observers over Paris fired rifles at French aircraft in the air. The French retaliated with automatic rifles. Later, machine guns mounted on the wing, shooting over the propeller, and located at various other positions on the airplane, were introduced. Next, guns were synchronized to fire through the propeller. From then on, Germans and Allies increased the firepower of their aircraft. The French used the first cannon, a 37-mm Hotchkiss, on the Voisin airplane. Guynemer, the French ace, used a similar cannon, firing through the propeller shaft of a Hisso engine in a Spad. It proved effective against aircraft and balloons. Leak-proof gasoline tanks and armor plate came too late for practical application in the war.

Records of these actions were shelved in War Department files until preparation for the current war brought them out again. Although aircraft were faster and more maneuverable when war came to the world in September, 1939, it caught American warplanes with their flaps down. Armament had not kept pace.

The few fighting planes that we had at that time were woefully lacking in firepower. Some of our fighter types had only one .30-caliber gun and one .50-caliber gun mounted side by side, firing through the propeller. These ships became obsolete overnight when World War II ushered in the era of the "flying gun platform." We had powerful bombers and speedy fighters in the works, however.

Creating this heavy firepower and at the same time adapting idea changes from the operational theaters is the job of the Materiel Command's Engineering Division Armament Laboratory at Wright Field.

War greatly accelerated the laboratory's task. Once a small, three-room office buried in the midst of hangars and shops at Wright Field, this laboratory was fed millions of dollars for experimental purposes and expanded into the largest aeronautical armament research center in the world.

Aircraft fire control is a new art. This war's trend toward a battlefield in the stratosphere has spawned heretofore untried types of aircraft armament. One solution is the use of remote fire control systems which remove the gunner from the proximity of his guns, diminishing the effects of vibration on the sighting operation and allowing the gunner greater comfort and less fatigue.

Paralleling the development of these remote control systems, high priority is being given to heavier-caliber guns and cannon for such installations.

Great advancement has been made in applying heavy-caliber cannon for fighter offensive use and as defensive installations in bombers. Much stress has been placed on power-driven turrets for all sizes of machine guns and cannon. Such installations include locally-operated, remotely-controlled and power-boosted hand-held mounts. The latter are vast improvements over original single hand- held flexible guns and enable the larger-caliber, multiple weapons to be more accurately controlled and sighted free from slipstream effect encountered at high speeds. These installations and their continued improvement have done a great deal toward commanding respect from enemy fighters.

For example, just after Pearl Harbor. the Japs found Fortresses without tail guns easy prey and accounted for several of the bombers by rear attacks. Two .50-caliber guns were installed in the Fortress tail and on one particular flight (the first time the new guns were used in combat), the tail gunner of one Fortress shot down seven Jap fighter planes. These early installations have been improved so that today tail gunners have more firepower and, in some cases, turrets have replaced the flexible guns. This increases effectiveness since turret fire is more accurate than the hand-held gun with its excessive vibration.

Machine guns fire from 600 to 1,200 rounds of ammunition per minute, depending upon the type of gun, caliber, temperature, synchronization and the design and location of all accessories such as feed chutes, ammunition boxes and means of ejection. However, rate of fire must not be over-emphasized. Guns are rarely fired in long bursts. In air combat a pilot seldom holds his trigger for bursts that exceed 25 rounds. If fire duration is exceeded, guns will become overheated and unintentional firing, damaged barrels and other serious malfunctions will result.

What constitutes adequate firepower for modern aircraft frequently becomes the object of discussion among those not familiar with this all-important factor in air warfare. The mere presence of numbers of guns or cannon, irrespective of caliber, is not indicative of true firepower. Each airplane must necessarily be treated separately during its initial design when every conceivable consideration is given to the number of weapons, their caliber and, above all, their placement in the aircraft to assure maximum protection.

We have been fortunate in having a wide range in aircraft weapon sizes — from the small .30-caliber machine gun, capable of firing 1,200 rounds per minute and weighing less than 25 pounds, to the larger cannon which fires at a much slower rate. However, American firepower today is relying on the .50-caliber machine gun. It is the weapon most commonly employed in our aircraft.

This gun, hailed as the finest arm of its kind in the world, weighs approximately 65 pounds and is capable of firing 800 rounds per minute. Relatively small in size, it fits easily into all our aircraft types. The projectile leaving the muzzle at a speed of over 2,900 feet per second can penetrate any kind and all parts of an airplane. And the shell is small enough for as many as 1,000 rounds per gun to be carried. During one test the .50-caliber was fired at an obsolete bomber fuselage. It smashed the bomber's skin, ammunition boxes, a longeron, a hard pine board and then pierced a 7/16-inch piece of armor plate.

The .50-caliber gun has an effective range of four miles and from that distance still packs sufficient wallop to kill a man. Another measure of its force can be brought out when it is estimated that bullets from the eight guns on a Republic Thunderbolt firing together deliver to an enemy target more horsepower punch than the 2,000-hp engine which pulls the ship through the air.

The number of guns carried in an airplane depends largely on the plane's configuration. In bomber types the guns usually are mounted in pairs which are disposed from nose to tail to afford protection from every conceivable direction of attack. In fighter types the number of guns varies from four to eight.

By comparison, a flight of 13 Republic Thunderbolts, each with eight .50-caliber guns, has three times the striking power of a machine gun unit of a German infantry regiment. A formation of 13 bombers, carrying a new heavy cannon now going on some of the medium types, carries twice the firepower of the 75-mm howitzer used by the Nazi regiment. A single flight of 13 Airacobras, carrying 37-mm cannon, is equal to the anti-tank guns of the regiment.

Downing an airplane with gun fire is not simple; it is difficult to keep a fast-moving target in range. A gunner must fire more rounds in a given time interval to assure a hit on a speeding airplane. In one sense the perfection of the machinery used by the gunner can be considered a measure of his firepower. If the gunner could be assured a hit each time he squeezed the trigger, obviously one gun would be adequate. However, because of the complications involved — the ballistic behavior induced when a projectile is fired from an airplane, the human element, and the speed and maneuverability of the airplane target — aerial gunnery is a complicated procedure.

Our bombers for some time have been using computing sights which have forced enemy fighters to remain at a range from which their firepower is ineffective. These computing sights are being improved continually. The problems involved in correcting completely for aircraft gun-laying are many and, to obtain hits, they must be solved to a fine degree of accuracy. These solutions include accurate and instantaneous computation of and correction for lead and ballistic variations caused by altitude, range and speed of the firing airplanes. In fact the corrections obtained through use of computers parallel those of the secret bombsight but actually involve a greater number of factors which must be solved with even less assistance from the gunner.

In the last war the ordinary ring and bead sight was standard for all aircraft guns. Now the ring and bead sight is used only on hand-held guns. Reflector sights eliminate the need for lining up the gunner's eye and front and rear sights with the target since the sight itself actually projects a sight reticle image onto a transparent reflector plate which, at infinity, moves with the gunner's eye. Thus, although the gunner's head may be in continual movement due to the passage of the plane through rough air, the sight line and target remain together.

Although the use of computing sights thus far has been limited to turrets, additional computing sights have been developed and placed in production for use in all other gun positions. A large amount of credit is due the various fire control system manufacturers for their research and development.

The gunsight aiming-point camera is proving highly beneficial in improving the accuracy of our gunners. A small compact camera, carrying 16-mm motion picture film in its magazine, it is mounted behind the gunsight and takes a picture of the sight reticle as it is projected on the target. Thus it is possible to study exactly what the gunner has seen through the gunsight and make evaluations and corrections to improve his aim. Quick-processing film enables this study to be made a few minutes after the gunnery practice — or actual air combat — since some of the cameras have already been employed in battle areas. While the gunner's errors are still fresh in his mind he can see what should have been done to improve his effectiveness.

Recently, instructors at a gunnery school revealed that before using the gun camera their students scored 22.4 per cent hits in ground gunnery and 4.7 per cent hits in aerial gunnery, but after they had used the camera and studied their faults, the hit percentage was jumped to 27.5 per cent for ground gunnery and 43.5 per cent for aerial gunnery. Later, in trying for gunnery records, those trained on the gun camera scored 58.75 per cent on ground gunnery and 59.5 per cent for aerial gunnery. Thirty per cent of gunners have been rated as experts after being trained in use of this camera.

Two main factors in aerial gunnery determine the accuracy of gun fire following automatic computation — tracking and ranging. Unless the gunner tracks smoothly and ranges precisely, the computing gunsight will be given inaccurate data on which to base its calculation. Tracking involves keeping the gunsight precisely on the target without deviation, while ranging refers to manipulation of the sight's range-measuring mechanism to keep the correct range constantly in the computer. Both are done in turrets by wrist or feet movements.

Advancements in aircraft armament over the past four years have necessitated the development of new armament testing facilities including indoor and outdoor firing ranges, cold rooms for test firing at extremely frigid temperatures, high altitude pressure chambers, sight and computer testing devices and advanced electronic tests. Because our aircraft are fighting in extremely high desert temperatures and extremely low arctic temperatures, it has been necessary to design armament equipment for perfect operation in all climatic and atmospheric conditions. The temperatures under which armament items are tested range from -60° to 160°. A recently completed cold test firing room at the Wright Field armament laboratory is proving invaluable in the investigation and testing of all equipment. In the high altitude pressurized chambers, strange phenomena of aircraft armament operation are being investigated continually.

From studies of the reaction of guns and their firing mechanisms to cold conditions, researchers have developed new greases and oils that allow smooth operation of guns at any temperature. They also have studied effects of cold and heat on the thick glass transparencies around windshields and turret installations and developed new types to offset the damaging temperatures. In another section of the large laboratory is a "torture test" chamber where guns are fired on life tests. Mounted on a large grotesque frame, machine guns and cannon are fired for as many as 8,000 to 10,000 rounds a day to determine life expectancy of gun barrels and to make sure there is no malfunction in the gun mechanism.

Such tests produce innovations in gun design and installation methods. Armament engineers, with the splendid cooperation of Ordnance, have worked out the most efficient guns in existence. In one day this year patent applications for seven new inventions on a particular gun were sent to Washington from the armament laboratory. The normal procedure in the development of new items of armament equipment involves the following steps: Requirements are laid down — usually as a result of actual combat requirements which are forwarded to the Materiel Command — and preliminary specifications drawn up by the armament laboratory. These specifications in most cases are submitted to competent fire control manufacturers who, in collaboration with engineers at Wright Field, conduct the necessary research development, design and fabrication of an experimental article. When the first model is completed, tests are made by the manufacturer prior to its release to the Materiel Command for further laboratory trials and installation in aircraft for preliminary air-firing.

Upon satisfactory completion of this testing, the model is sent to the Army Air Forces Proving Ground Command at Eglin Field where complete functional and tactical suitability tests are carried out. If the article under test meets the requirements it is recommended for standardization and procurement. This may seem a long drawn-out routine but actually it is accomplished in a relatively short time.

Conversion of the Douglas attack bomber into a night fighter was an example of meeting the demands from the front. For some time the British were using Bostons on intruder raids over the Continent — going over low, skirting between hills, and dropping light fragmentation bombs on German airfields and gun installations in France. But this wasn't enough. The British wanted the plane for a fighter as well. They tried different types of gun installations in the nose of the ships. We have followed suit in converting this plane, which we call the Havoc.

Changes in armament usually mean long, drawn-out conferences behind closed doors — hard, cold fact discussions with experts from the equipment laboratory who tell us how much electrical energy we need for new installations, how much we can get and no more. Gun engineers, crack turret trouble shooters, bomb and bombsight technicians are present. We discuss the whole idea with the men who operate our training schools, teach our bombardiers and gunners. Then, from the aircraft laboratory specialists, we learn how much airplane we can cut away for new installations; how much weight we can add here and take off there to keep the plane aerodynamically stable Some time is spent with production division men who handle the task of getting needed materials, readying a manufacturer to build the plane we desire and seeing to it that production begins immediately.

After standardization and procurement of new armament equipment, work is continued by the manufacturer and the armament laboratory to improve the article still further. Indicating the scope of experimental projects concurrently undergoing development and testing by armament experts, there are at present approximately 70 airplanes of different types at Wright and Eglin Fields. In some cases, upon completion of the tests by Eglin Field, the airplane and experimental armament items are flown to a combat zone for further tactical evaluation before they go into actual service. All armament development projects do not originate with tactical organizations. The initiation of a new experimental airplane in most cases calls for a parallel development program by the armament laboratory.

To illustrate how a new airplane may dictate new armament designs, it may be said that plans for the giant Douglas B-19 bomber called for unprecedented turret installations — before the British or any other country turned attention to the power-operated turret. The armament laboratory's task was to design, perfect and install these turrets in mock-ups long before the big plane took to the sky. Thus, contrary to popular belief, American designers were studying the effectiveness of mechanically controlled turrets some time before the war.

Types of armament are determined by the tactical use to be made of the airplane. For instance, in the case of a night fighter where the normal technique requires approach on the target from a certain direction, the fire control equipment must be so designed that the maximum firepower can be obtained in that direction. The sight operator's position must be located to permit maximum visibility in scanning and sighting. In the case of the night fighter, development of a sight that allows greater passage of light through the optical system may be required.

One night fighter developmental design has a multiple-gun turret. For several months we tested the turrets in special mock-ups in our laboratory before the complete airplane was brought to Wright Field. The plane's upper turret fairly bristles with guns, resembling an infantry pill box.

In the past, the main function of the armament laboratory was to develop new aircraft armament items. In addition to this development work, much of the effort of this laboratory — and of the Engineering Division — is directed toward the modification of combat equipment to replace one type of standard equipment with another type, depending on the tactical use of the aircraft. Other developments engineered by the armament laboratory may not be for specific application — but for insurance against the day they are needed. Some of our newest gadgets are put on the shelf to await the time when they can be used most effectively.

Up to the present time, armament for fighter aircraft has varied only in caliber of guns. However, with the stepped-up tempo of enemy fighter activity, the requirement for a fixed gun installation that will provide automatic corrections for lead, range, altitudes and speeds is becoming more apparent. This subject now is being investigated and development models are being tested. A great amount of development work also is being accomplished on new improved types of fighter gunsights. These include sights for night fighting purposes, extension of present sighting ranges, combination gunsights and dive bombsights.

That the firepower job is being well done is evidenced by the tallies which our airmen are scoring in combat against the enemy, by the number of Jap and German planes falling in combat, and the ever-increasing pounding of enemy cities by our big bombing planes. Literally, we are designing guns and putting wings on them.

This article was originally published in the June, 1944, issue of Flying magazine, vol 34, no 6, pp 58, 104, 106, 110, 114.
The PDF of this article includes a photo of a P-47 at a firing range.
Photo credited to Republic.