Aircraft Gunner

The Oerlikon 20 mm cannon is a series of autocannons, based on an original German Becker Type M2 20 mm cannon design that appeared very early in World War I.It was widely produced by Oerlikon Contraves and others, with various models employed by both Allied and Axis forces during World War II, and many versions are still in use today. Aim of enemy fighter is to destroy; aim of bomber air gunner is to get safely to target and back to base. Never fire until fired upon; If gun fire, search for fighter; take evasive action. Always watch your own tail. Conserve your ammo; if you’re fired upon from long range, instruct pilot to use evasive action.

A ball turret was a spherical-shaped, altazimuth mountgun turret, fitted to some American-built aircraft during World War II. The name arose from the turret's spherical housing.

It was a manned turret, as distinct from remote-controlled turrets also in use. The turret held the gunner, two heavy machine guns, ammunition, and sights. The Sperry Corporation designed ventral versions that became the most common version; thus, the term 'ball turret' generally indicates these versions.

Sperry ball turret[edit]

Sperry and Emerson Electric each developed a ball turret, and the designs were similar in the nose turret version. Development of the spherical Emerson was halted. The Sperry nose turret was tested and preferred, but its use was limited due to poor availability of suitable aircraft designs. The Sperry-designed ventral system saw widespread use and production, including much sub-contracting. The design was mainly deployed on the B-17 Flying Fortress and the B-24 Liberator, as well as the United States Navy's Liberator, the PB4Y-1.The ventral turret was used in tandem in the Convair B-32, successor to the B-24. Ball turrets appeared in the nose and tail as well as the nose of the final series B-24.

The Sperry ball turret was very small^{[clarification needed]} in order to reduce drag, and was typically operated by the smallest man of the crew. To enter the turret, the turret was moved until the guns were pointed straight down. The gunner placed his feet in the heel rests and occupied his cramped station. He would put on a safety strap and close and lock the turret door. There was no room inside for a parachute, which was left in the cabin above the turret. A few gunners wore a chest parachute.

The gunner was forced to assume a fetal position within the turret with his back and head against the rear wall, his hips at the bottom, and his legs held in mid-air by two footrests on the front wall. This left him positioned with his eyes roughly level with the pair of light-barrel Browning AN/M2 .50 caliber machine guns which extended through the entire turret, located to either side of the gunner. The cocking handles were located too close to the gunner to be operated easily, so a cable was attached to the handle through pulleys to a handle near the front of the turret. Another factor was that not all stoppages could be corrected by charging (cocking) the guns. In many cases, when a stoppage occurred, it was necessary for the gunner to 'reload' the gun, which required access to the firing chamber of the guns. Access was severely restricted by the guns' location in the small turret. Normally, the gunner accessed the firing chamber by releasing a latch and raising the cover to a position perpendicular to the gun but this was not possible in the ball turret. To remedy that, the front end of the cover was 'slotted'. The gunner released the latch and removed the cover which allowed space to clear the action. Small ammunition boxes rested on the top of the turret and additional ammunition belts fed the turret by means of a chute system. A reflector sight was hung from the top of the turret, positioned roughly between the gunner's feet.

In the case of the B-24, the Liberator's tricycle landing gear design mandated that its A-13 model Sperry ball turret have a fully retractable mount, so that the ball turret would always be retracted upwards into the lower fuselage while the aircraft was on the ground, providing ground clearance with it in the stowed position. The conventional landing gear of the B-17 meant that the ball turret did not need to be retracted for clearance on the ground, but if the plane was required to do a belly landing (such as in the case of landing gear system failure), the ball turret would likely be destroyed due to the lack of clearance, meaning anyone occupying the turret would be in a precarious position if unable to escape.

ERCO ball turret[edit]

After testing in mid-1943, the ERCO ball turret became the preferred bow installation in the Navy's Consolidated PB4Y-1 Liberator and PB4Y-2 Privateer patrol bombers although other types continued to be installed. Earlier designs appeared in other patrol seaplanes. It served a double purpose, defense against bow attacks as well as fire suppression and offensive strafing in antisubmarine warfare. Since this turret is of the ball type, the gunner moves with his guns and sight in elevation and azimuth by means of control handles. Among the earlier designs was the Martin 250SH bow turret of the PBM-3 twin-engined patrol flying boat which had many points of similarity in design and action.

Popular culture[edit]

• A ball turret features in the poem 'The Death of the Ball Turret Gunner', by Randall Jarrell.
• The father of T.S. Garp, the main protagonist in John Irving's fourth novel The World According to Garp (1978), is a severely injured ball turret gunner.
• In 'The Mission,' a 1985 episode of the television series Amazing Stories, a young ball turret gunner is trapped in his turret until his skill as a cartoonist saves him.

References[edit]

External links[edit]

• Pastor, Iris Ruth (November 11, 2015). 'My Dad was a Ball Turret Gunner'. Huffington Post. Retrieved November 11, 2015.

A Oerlikon gunner at his gun mount aboard the in 1942The Oerlikon FF was installed as armament on some fighters of the 1930s, such as the Polish G. Locally produced derivatives of the Oerlikon cannon were used much more extensively, on aircraft, on ships and on land. In the air, the Ikaria was used as armament on a number of German aircraft, of which the most famous is the.

The Japanese Navy similarly used their copy of the FF, designated the on a number of types including the. Later in the war, they also equipped fighters including the Zero with the, a version of the more powerful and faster-firing Oerlikon FFL.The French firm of Hispano-Suiza was a manufacturer of aircraft engines, and it marketed the moteur-canon combination of its and engines with a or cannon installed between the cylinder banks. The gun fired through the hollow propeller hub, this being elevated above the crankcase by the design of the gearing. Such armament was installed on the and some other types. Similar German installations of the MG FF were not successful.

Diagrams showing basic design and colour-coding of British HE/Incendiary, Tracer and HE/Incendiary/Tracer shells for the 20 mm Oerlikon gunThe Oerlikon became best known in its naval applications. Initially the Oerlikon was not looked upon favorably by the as a short-range gun. All through 1937-1938 Lord, then a in the Royal Navy, waged a lone campaign within the Royal Navy to set up an unprejudiced trial for the Oerlikon 20 mm gun, but it was all in vain.

It was not until the of the, was appointed that Mountbatten's efforts bore fruit. During the first half of 1939 a contract for 1,500 guns was placed in Switzerland. However, due to delays and then later the in June 1940, only 109 guns reached the United Kingdom.

All Oerlikon guns imported from Switzerland, in 1940, were mounted on various gun carriages to serve as light AA-guns on land.Just a few weeks before the Fall of France, the Oerlikon factory approved manufacture of their gun in the United Kingdom, under licence. The Royal Navy managed to smuggle out the necessary drawings and documents from. The production of the first British-made Oerlikon guns started in, at the end of 1940. The first guns were delivered to the Royal Navy in March or April, 1941.

The made extensive use of Oerlikon guns in the anti-aircraft role. These were the principal armament for its Light Anti-Aircraft squadrons in North Africa, the Middle East, Italy, and North Western Europe, until the introduction of the 40/L60 40mm gun from 1943, although many squadrons retained a mix of guns until the end of World War 2. Squadrons in the Far East were equipped exclusively with Oerlikons.

1945, a row of 20 mm Oerlikon guns aboard theThe Oerlikon gun was installed aboard ships from 1942, replacing the, which lacked range and firepower, and largely superseding the, which was heavier and had less mechanical reliability. It became famous in the naval anti-aircraft role, providing an effective defense at short ranges (in practice up to 1.5 km) at which heavier guns had difficulty tracking a target. The gun was eventually abandoned as a major anti-air weapon due to its lack of against heavy aircraft and against Japanese attacks during the. It was largely superseded by the gun and the. It provided a useful increase in firepower over the.50 cal machine gun when adapted and fitted to some aircraft. However, it had some problems with jamming in the ammunition feed.The popularized the use of the Oerlikon gun as an anti-ship and anti-submarine gun - while it was not effective against the armour of most larger ships, it was used extensively and effectively against, and on the decks of larger ships. A handful of were fitted with the weapon toward the end of the war, but it appeared more commonly on and at the time.The Oerlikon was also used as the basis for the gun, designed by Polish engineers in exile in the United Kingdom.

The gun went into service in 1944, and was used well into the 1950s, among other uses, on and early model.Romania purchased 45 pieces from Germany during the first half of World War II. Post-war. The aiming sight of the Oerlikon gunVery unusually for a high-powered autocannon, the Oerlikon and its derivatives feature operation: the bolt is not locked to the breech of the gun at the moment of firing.

Non-locking, simple blowback designs are commonplace in much lighter weapons, such as small-caliber semi-automatic pistols. No locking is required, as with such low-power cartridges the static inertia of the bolt or bolt and slide - the physical tendency of heavy components to resist rapid acceleration - is adequate to ensure that the projectile has left the muzzle and the gas pressure in the barrel is down to a safe level before the breech opens (while the bolt spring also resists the opening of the breech, in practical terms its contribution is too small to be relevant). In contrast, 20mm cartridges are far too powerful, and efficient autocannon barrels too long, for this basic system to be practical; so the Oerlikon uses (API) to augment the resistance of the bolt. In API blowback weapons, the firing pin fires the cartridge while the bolt is still traveling forward so that the gas pressure has to overcome the forward momentum of the bolt as well, before it can push it to the rear. To facilitate this, the Oerlikon's chamber is longer than needed to contain the cartridge, and the end of the bolt, which is the same diameter as the case, actually enters this extended chamber behind the cartridge before firing. As a result, when firing occurs, the forward force of the bolt and spring acts against the force of the propellant gases until the latter overcome the former and start pushing case, bolt and spring backwards. If the bolt had stopped at the mouth of the chamber as in a simple blowback gun, this momentum would be neutralized and the additional forward oppositional force would not exist.

A second advantage of this unusual arrangement is that after firing, the bolt and case have a short, but significant, distance to travel rearwards before the bolt-end re-emerges and the case in turn begins to leave the chamber—providing more time for gas pressure to drop to the necessary safe level. This system permits blowback to be used in far more powerful weapons than normal. Nevertheless, compared to guns with a locking mechanism a fairly heavy bolt must be employed; while to give this heavy bolt sufficient forward speed, a large spring is required (and Oerlikons, distinctively, have this component wrapped around their barrels.) These features will limit the rate of fire of such guns, unless other steps are taken—as in the final model of the.This unique chamber and bolt design necessitates the use of a characteristically shaped cartridge: the case has straight sides, very little neck, and a. The straight sides allows the case to slide back and forward in the cylindrical chamber.

The neck is not supported while this happens and therefore expands when the case is fired, and the rebated rim allows the face of the bolt, with its extractor claw hooked over the rim, to fit within the chamber. To ease the motion of the case, the ammunition needed to be greased, which was a drawback of the Oerlikon cannon.

An alternative developed during World War II was the so-called fluted chamber, which had grooves that allowed propellant gas to seep between the chamber wall and the case, taking over the role of the grease. A twin Oerlikon gun mount from theAmmunition feed is typically by a 60-round drum on the top of the gun. During sustained firing, the magazine must be frequently changed, reducing the effective rate of fire.

Magical vacation travels. Belt-fed versions of the gun were developed to overcome this limitation. A trigger in the right-hand grip controls fire.

Used cartridges are ejected from below the breech.Different nations and services operated a number of mounting types for the same basic gun. In a typical single-barrel naval version, it is free-swinging on a fixed mounting with a flat shield affording some protection for the crew.

The cannon is aimed and fired by a gunner using, in its simplest form, a ring-and-bead. The gunner is attached to the weapon by a waist-belt and shoulder supports. For this reason, some mountings existed with a height-adjustment feature to compensate for different sized gunners.

A 'piece chief' designates targets and the feeder changes exhausted magazines.During World War II, twin and quadruple Oerlikon mounts were developed, both for army and for navy use. The British Navy operated a hydraulically operated twin-gun mount. The US Navy operated a quad mount developed for by Elco Naval Division, Electric Boat Company, called the Elco 'Thunderbolt' Mount.

Prototypes were built and tested in late 1942 and operationally deployed on several Elco PT Boats in the Mediterranean. It was also placed experimentally on the battleships, and training ship.See also.References.