The Ball Turret – a Vertigo Sufferers Nightmare

A bomber’s ball turret position is often looked at with fear in ones eyes, being suspended underneath a bomber with 30,000 ft between you and the ground. The turret was a small, cramped place to be, often operated by the smallest men available.

It was named the Sperry turret, after the company that made it; the Sperry Corporation.

They were most famously used on the Boeing B-17 Flying Fortress, but also saw use on the B-24 Liberator bomber.

The ball turret on a B-17G. Image by JustSomePics CC BY-SA 4.0

The Ball Turret’s Origin

The B-17 was not originally designed with a ball turret. Early models had very different defensive setup.

Early B-17 models A and B used blister canopies on the waist section of the fuselage armed with machine guns. The underside was protected by another blister with a single machine gun.

The waist blisters caused considerable drag and disturbed airflow, while limiting the gunners traverse. These were removed in the B-17C and replaced with flush windows.

The B-17C also changed the belly defence to a ‘bath tub’ type, similar to the German Heinkel 111. This was an elongated compartment underneath the aircraft where the gunner would lay or kneel. From here, the gunner could protect the rear section below the plane.

An early B-17C. Note the ‘bathtub’ gunner position.

In the 1941 B-17E model, the tub was replaced with the famous ball turret. The turret could turn on two axis; 360 degrees horizontally and 90 degrees vertically. The system allowed the gunner to protect all of the bottom area under the aircraft, instead of just the rear.

How it Worked

The turret was attached to a strong support beam on the top of the aircraft’s fuselage. Its movement was controlled by a self contained electrically powered hydraulic system, and could rotate at high speeds; important for tracking fast moving enemy aircraft.

It moved horizontally by a ring gear on the turret. A trunnion system is mounted to the ring gear that allowed vertical and horizontal movement at the same time.

The turret outside the aircraft showing the ring gear.

Entering the Turret

The ball’s door was located directly behind the gunner, so with the guns at 0 degrees vertical, the turret could technically be entered from the outside while the B-17 was on the ground. However, since there was only 40 cm between the ball and the runway, gunners would wait until the aircraft was in flight before entering. This was the same for the return flight.

The door of the ball turret can be seen from above, inside the aircraft. Image by The PIPE CC BY-SA 4.0

B-24 Liberators were too low to the ground for the ball to fit. They were fitted with a retractable turret, allowing it to be stowed away for take off and landing.

To enter in flight, the gunner had to manually traverse the turret so the guns were pointing directly down, allowing access to the door. Once in, the door was closed shut, and he placed his feet into stirrups in front of him, and held the triggers above his head. His position resembled the fetal position. On the ends of the grips were the buttons to fire the guns.

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Operating the Turret

The gunner looked through the central hole between the guns to aim. He was shielded by an armour plate in front of him. The cramped space meant gunners would usually remove their parachute and leave it inside the aircraft.

For defence, two Browning AN/M2 .50 calibre machine guns were squeezed into the turret either side of the gunner. This provided some incredible firepower. The AN/M2 guns were lightened versions of the ground based M2 machine gun, with a rate of fire of 600-800 rounds per minute each.

To aim the guns, the Sperry turrets were equipped with the advanced K-4 gun sight. It mounted above and in front of the gunner’s head, so its reticle would be in line with his eyes. The K-4 sight worked by using data inputs from the gunner to calculate the required deflection (lead).

The gunner would use his left foot to adjust a frame in the sight to match the size of the targets wings, this would provide the targets range to the sight. Via input shafts from the ring gear, the K-4 then used the turret’s horizontal and vertical speed to estimate the targets speed. With this information, the K-4 reticle would automatically adjust to the lead required to hit the target. For 1941, this was cutting edge technology.

The cramped space and K-4 sight can be seen from this view inside. Image by Mr.Z-man CC BY-SA 3.0

Bomber Crews

As with all roles in the B-17, the ball turret gunner needed to be fearless. He can look out of his porthole straight down for almost 6 miles, while battling incoming aircraft, sealed inside an aluminium ball without a parachute.

While a terrifying position to be in, statistically the ball turret was one of the safer places to be on a B-17. The compact size of the gunner surrounded by thick glass, aluminium and armour plating, combined with being underneath the aircraft, meant the gunner was relatively safe.

This however quickly flips when the aircraft is shot down, as the gunner has to turn to the turret to the exit position, climb out, and put on his parachute, all while the aircraft is falling out the sky.

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Ball turrets were eventually abandoned in later aircraft in favour of remote controlled systems, and then radar aimed turrets in aircraft like the B-52. The last aircraft shot down by a defensive gunner was in 1972, where a B-52 tail gunner shot down a MIG-21 over Vietnam.