Aircraft Power Turrets

A discussion of power-driven turrets to inform the maintenance mechanics who must service and repair our flying forts

By Carl K. Ryal

Technical Sergeant
(Phase Supervisor, Power Turrets; Lowry Field, Denver, Colorado)

Air superiority, as indicated by current war records, depends not only on getting ships into the air but on keeping them there. Outproducing the Axis in the field of aircraft may turn out to be a hollow victory if the ships prove incapable of properly defending themselves once they are over enemy territory.

The overall box score of United Nations bombers has been remarkably good. Compared to the losses incurred in combat by Axis heavy and medium bombers, both British, Russian and American "heavies" have come through virtually unscathed. A side-by-side examination of parallel types of Axis and United Nations bombers shows one feature: power turrets — a system of mounting armament on a rotatable mounting in such a manner as to afford complete directional freedom of action yet, at the same time, drive the gun to firing position with greater pressure and steadiness than manual operation could afford.

Historically, power-driven turrets date back to improvements in high-speed bombers. The Boulton-Paul company in England, in the early thirties, produced a fast, twin-engined bomber called the Overstrand. This ship carried its defensive armament in the places considered conventional at the time — on Scarff mounts in the nose of the plane and atop the fuselage, midway between the pilot's cockpit and the tail.

The Overstrand was a great success — too great. Its top speed was somewhere over 180 mph; phenomenal for its time. Only one thing was wrong. It was virtually impossible to shoot accurately from either of the gun positions. In the wind-swept cockpits, gunners had to struggle for dear life to keep from being blown out, and having established a grip on themselves, found it tougher still to keep the gun itself from being swung out of firing alignment.

It became evident immediately that two things had to be done: physical protection had to be provided for the gunner, and power and steadiness, greater than that which the human frame could furnish, had to be mechanically created.

The next Boulton-Paul model to emerge, the Sidestrand, came out with a "greenhouse" in front, streamlined into the ship's oval section. Experiments on power-driven turrets took various form. The first Boulton-Paul units had the serio-comic "zipper slit"; the vertical gap in which the .303 Lewis gun moved up and down was closed by two strips of cloth closed by a standard talon fastener. The key, or meshing units were attached above and below the barrel, opening and closing the zipper as the gun changed angles. While this made the turret windtight, it proved more trouble than it was worth.

British Frazier-Nash and Boulton-Paul turrets evolved during the period when Britain struggled to prepare for the current conflict. The full tail turret was first put into standard production on the Armstrong-Whitworth Whitley. The idea of having a tail gun position behind the tail surfaces dates back to the old Vickers Virginia and saw experimental use during the last days of World War I.

Parallel development began in Russia shortly after Britain exhibited her first units, and their presence was noted during the Finnish campaign. The Glenn L Martin Co, working on English contracts, began building their own power turrets shortly thereafter. Then other US companies followed suit.

The actual outbreak of war saw turrets on most of the British heavy bombers and on the shocking little two-seater, the Boulton-Paul Defiant. This ship, as the enemy has since discovered, carried a full turret mounting four rifle-calibered machine guns. One squadron, operating at Dunkirk with Defiants, knocked down 37 Ju-87s without loss to themselves.

The turrets manufactured by the British, efficient though they have proven, have acquired almost incredible mechanical refinement since May, 1940, but their basic hydraulic principle is still unaltered and still shares the spotlight with the more recent electrically driven types. Both have their advantages and their champions.

The effectiveness of power turrets lies in increased accuracy with less fatigue for the gunner. Simple manipulation of light control handles will swing heavy caliber guns around in varying slipstream pressures at a constant speed with little human effort. This is particularly important in high-altitude fighting where physical efficiency reaches low ebb and mental reactions are slowed. The computing sights now used in many turrets relieve the gunner of almost all guesswork and calculations, and the scoring of direct hits at ranges up to 1000 yards has been reduced to the fundamentals of framing a target in the sight and pressing the triggers.

As a defensive weapon, the power turret has provided a revolutionary answer to the problem of bomber protection. Heavily armed bombers can now throw out such a withering curtain of fire power that they make unhealthy quarry for attacking ships, and accordingly a fighter escort is not required. American bombers are consistently demonstrating their self-sufficiency by making spectacular daylight raids over France, unaccompanied, and the negligible losses attest to their ability to protect themselves in hostile territory.

Obviously, the more turret positions a plane can accommodate, the more protection it will enjoy. Although our medium bombers are too small to permit a turret installation in the tail, the B-25, for example, mounts upper and lower turrets which afford almost complete defense. The guns of the upper turret can cover the entire area above the plane, down to horizontal level, while the lower turret guns not only protect the full underside range but also extend their fire area several degrees above horizontal. This means the two paths of fire may be brought to converge a short distance behind the tail of the plane, with deadly results.

The only tail turret being used to any extent at present is the Consolidated, mounted in a B-24. This is a fairly simple chamber, housing the gunner, sights and guns, rotating on a vertical axis. Its advantage lies in perfect vision to the rear of the plane, with nothing to obstruct the fire-path of its two guns.

Nose turrets for our heavy bombers are a fairly recent innovation and are still in the stage of development, but experiments are being made on these units with various degrees of armament, and they are expected to be standard equipment in the near future.

To date we have made extensive use of two types of lower turrets: the Sperry Ball, and the Bendix. As its name implies, the Sperry is designed as a sphere, and is installed in the bellies of our B-17 series of heavy bombers, enclosing the gunner and his armament. The unit is operated hydraulically, and the turret moves freely in all directions in response to a light touch on the control handles.

The Bendix Lower operates upon an entirely different principle. It is a retractable unit which may be lowered beneath the plane for operation, or pulled up into the fuselage when not in use. This feature of retractability offers several unique advantages. First, it cuts down air resistance in flight, and secondly, it permits installation in some of our low-slung bombers which do not have sufficient landing clearance for ordinary belly turrets. The Bendix, unlike the Sperry Ball, does not house the gunner. The gunner operates this unit from a spot above it, within the fuselage, and tracks his target by means of a periscopic sight arrangement.

Our most popular upper turrets have been the Sperry, the Martin and the Bendix. They are all designed along similar lines, accommodating the gunner in a sitting or standing position, with convenient control handles located directly in front of him. The upper turrets are free to make a complete rotation in azimuth and the guns alone move in elevation.

Most of our present turrets are equipped with two .50-caliber machine guns which are fired electrically by pressing trigger switches located on the turret control handles. Large ammunition containers are usually located within the turret itself, providing sufficient ammunition capacity for almost any mission. Since it often requires considerable strength to charge .50-caliber guns in case of jamming, several types of mechanical chargers are being used in turrets. One method employs a system of cables and pulleys to produce charging leverage. Another system uses CO2 to drive a piston. Hydraulic chargers are also in use, operating in a manner similar to the CO2 method.

The fine machining and skillful construction of a power turret would do justice to the watch-maker's art. It is a tribute to engineering ingenuity that such a complicated piece of machinery is able to withstand the abuse of combat duty as well as it does. The Vickers hydraulic unit, heart of the Sperry turret, is a marvel of precision designing, and is one of the most amazing units for the smooth transmission of power yet developed. The involve electrical system of other turrets perform equally incredible tasks through a veritable network of circuits.

Impressive as power turrets are today, they are still in their infancy. Refinements and improvements which are pouring from the drafting tables daily make the present models look archaic. The trend now is towards "central fire control", an aerial adaptation of the battleship firing technique. One gunner located in a central sighting station will be able to manipulate all turrets by remote control. Targets will be tracked by computing sights with superhuman mechanical brains, and electric relays will pass the firing order from one turret to another as the target changes position.

Eliminating individual gunners from the turrets makes way for more armament and more ammunition. Turrets will mount four machine guns instead of two.

Some will be equipped with cannons. Planes bristling with six turrets will not be unusual, and their shattering fire power will fairly pulverize any luckless attacking plane which ventures within range.

This article was originally published in the March, 1943, issue of Air Tech magazine, vol 2, no 3, pp 19-21, 55.
Photos credited to Kulick, British Press Service, International, March of Time, Briggs, USAAFTTC.
The PDF of this article includes several photographs captioned: