10.12.2007, 19:52
OK, well I've read up on this and it seems there are some popular misconceptions to dispel.
The RAF fitted versions of their MkII Gyro sight to Lancaster rear and mid-upper turrets in 1944, but as the Lanc isn't in the game, we can move on. :wink:
American turrets were fitted with one of three types of sight:
i) The Type N-6a.
This sight had a simple circle and dot reticule, similar to the British GIIIa sight. It was used in the following:
Consolidated Model A6A and Emerson Model 111 tail turrets (B-24J)
B-17G Cheyenne tail gun positions
Some Bendix upper turrets (B-25 Mitchell)
Some Bendix chin turrets (B-17G).
Some Martin 250 mid upper turrets (B-24, B-26)
ii) The Type N-8 'retiflector'.
This sight had an unusual reticule - three rings and a central dot. It was used in the following:
Consolidated Model A-6 and Emerson Model 127 nose turrets (B-24 H & J)
Some Bendix upper turrets (B-25 Mitchell)
Some Bendix chin turrets (B-17G).
Some Martin 250 mid upper turrets (B-24, B-26)
iii) The Type K-3 (or K-4) Sperry lead-computing sight. (Not to be confused with a K-14 gyro sight - the K-3/4 was a simpler device).
The K-3 was fitted to all Sperry upper turrets. When inverted it was called the K-4 and fitted to all Sperry ball turrets:
Sperry ball turrets were fitted to B-17E, Fs and Gs and B-24H,J,M and Ns.
Sperry upper turrets were fitted to B-17E, Fs and Gs
So far as I can determine, the K-14 gyro sight was never fitted to American turrets - there was presumably no need as Sperry had already developed an effective lead-predicting sight in 1940/41. (See below). It was fitted to all Sperry upper and ball turrets from September 1941, but could not be retro-fitted to other makes because it was quite bulky. A turret had to be designed from the outset to accommodate it.
The Sperry K-3 (called the K-4 when inverted to fit ball turrets) gave the gunner a point to aim at allowing for range and deflection - providing the gunner tracked the target accurately. The gunner had to manually adjust the illuminated sighting graticule (with a twist grip or a foot pedal) and select the position of the aircraft-type indicator. This sight used a gyroscope to measure the rotational speed of the turret and the azimuth/elevation of the guns in order to calculate the required deflection. This was sufficient because American bombers did not jink all over the sky to avoid being attacked. Their doctrine was to stay in position in level flight, to gain the benefit of defensive fire within the combat box.
(In a K-14 the gyroscope was used as an accelerometer to measure the acceleration of the host aircraft in its attempts to stay on the tail of an enemy machine. This allowed it to predict the path of the enemy and provide a computed impact point).
What did the Sperry reticule look like? I found this description, written by an ex-B-17 gunner:
"The upper turret and the ball turret both used compensating sights that used an optical head. There was no zoom feature or color. They (the K-3 for the upper and the K-4 for the ball) had a viewing screen that used black line reticules. They consisted of a horizontal line in the center with 2 vertical lines that the gunner manipulated. The left line was from the horz. line up. The right line was from the horz. line down.
In aiming, the horiz. line was kept thru the middle of the fighter's fuselage. He manipulated the vert. lines to the wing tips of the fighter. The farthest distance to be considered in range was 1,000 yards. As the fighter neared the bomber the vertical lines were kept on his wing tips.
As the gunner did these operations, and tracked to keep the fighter on those lines, the compensating sight accomplished the necessary lead of the target.
The gunner had to identify his target type (ME 109, FW190, etc.), and had to know the wingspan. There was a dial on the right side of the sight, where the gunner entered the wingspan. He turned the turret so the horizontal line on the sight was through the target. He depressed the pedal until the vertical lines were on the wingtips of the target.
The sight was a compensating computer sight that worked from the speed of the turret motion...the gunner kept the reticule on the incoming fighter, and the rate of motion of the turret was translated into the necessary lead for the bullets to arrive at the target."
The only other important American system was the GE remote fire control system, fitted to the B-29. This used large optical sights linked to a central gunlaying computer to aim remote barbettes. The central computer (in an armoured box in the middle of the B-29) was fed information regarding the size of an approaching enemy machine and its speed by the gunner's sight. The computer measured the same variables as the Sperry sights but added others such as outside temperature (air density affected how far a round would travel) and parallax (caused by the fact that the guns were distant from the gunner) to provide deflection for the guns. All the gunner had to do was hold the sight on the target for a couple of seconds and fire, having set the enemy aircraft type on the dial. The computer would offset the guns automatically.
The RAF fitted versions of their MkII Gyro sight to Lancaster rear and mid-upper turrets in 1944, but as the Lanc isn't in the game, we can move on. :wink:
American turrets were fitted with one of three types of sight:
i) The Type N-6a.
This sight had a simple circle and dot reticule, similar to the British GIIIa sight. It was used in the following:
Consolidated Model A6A and Emerson Model 111 tail turrets (B-24J)
B-17G Cheyenne tail gun positions
Some Bendix upper turrets (B-25 Mitchell)
Some Bendix chin turrets (B-17G).
Some Martin 250 mid upper turrets (B-24, B-26)
ii) The Type N-8 'retiflector'.
This sight had an unusual reticule - three rings and a central dot. It was used in the following:
Consolidated Model A-6 and Emerson Model 127 nose turrets (B-24 H & J)
Some Bendix upper turrets (B-25 Mitchell)
Some Bendix chin turrets (B-17G).
Some Martin 250 mid upper turrets (B-24, B-26)
iii) The Type K-3 (or K-4) Sperry lead-computing sight. (Not to be confused with a K-14 gyro sight - the K-3/4 was a simpler device).
The K-3 was fitted to all Sperry upper turrets. When inverted it was called the K-4 and fitted to all Sperry ball turrets:
Sperry ball turrets were fitted to B-17E, Fs and Gs and B-24H,J,M and Ns.
Sperry upper turrets were fitted to B-17E, Fs and Gs
So far as I can determine, the K-14 gyro sight was never fitted to American turrets - there was presumably no need as Sperry had already developed an effective lead-predicting sight in 1940/41. (See below). It was fitted to all Sperry upper and ball turrets from September 1941, but could not be retro-fitted to other makes because it was quite bulky. A turret had to be designed from the outset to accommodate it.
The Sperry K-3 (called the K-4 when inverted to fit ball turrets) gave the gunner a point to aim at allowing for range and deflection - providing the gunner tracked the target accurately. The gunner had to manually adjust the illuminated sighting graticule (with a twist grip or a foot pedal) and select the position of the aircraft-type indicator. This sight used a gyroscope to measure the rotational speed of the turret and the azimuth/elevation of the guns in order to calculate the required deflection. This was sufficient because American bombers did not jink all over the sky to avoid being attacked. Their doctrine was to stay in position in level flight, to gain the benefit of defensive fire within the combat box.
(In a K-14 the gyroscope was used as an accelerometer to measure the acceleration of the host aircraft in its attempts to stay on the tail of an enemy machine. This allowed it to predict the path of the enemy and provide a computed impact point).
What did the Sperry reticule look like? I found this description, written by an ex-B-17 gunner:
"The upper turret and the ball turret both used compensating sights that used an optical head. There was no zoom feature or color. They (the K-3 for the upper and the K-4 for the ball) had a viewing screen that used black line reticules. They consisted of a horizontal line in the center with 2 vertical lines that the gunner manipulated. The left line was from the horz. line up. The right line was from the horz. line down.
In aiming, the horiz. line was kept thru the middle of the fighter's fuselage. He manipulated the vert. lines to the wing tips of the fighter. The farthest distance to be considered in range was 1,000 yards. As the fighter neared the bomber the vertical lines were kept on his wing tips.
As the gunner did these operations, and tracked to keep the fighter on those lines, the compensating sight accomplished the necessary lead of the target.
The gunner had to identify his target type (ME 109, FW190, etc.), and had to know the wingspan. There was a dial on the right side of the sight, where the gunner entered the wingspan. He turned the turret so the horizontal line on the sight was through the target. He depressed the pedal until the vertical lines were on the wingtips of the target.
The sight was a compensating computer sight that worked from the speed of the turret motion...the gunner kept the reticule on the incoming fighter, and the rate of motion of the turret was translated into the necessary lead for the bullets to arrive at the target."
The only other important American system was the GE remote fire control system, fitted to the B-29. This used large optical sights linked to a central gunlaying computer to aim remote barbettes. The central computer (in an armoured box in the middle of the B-29) was fed information regarding the size of an approaching enemy machine and its speed by the gunner's sight. The computer measured the same variables as the Sperry sights but added others such as outside temperature (air density affected how far a round would travel) and parallax (caused by the fact that the guns were distant from the gunner) to provide deflection for the guns. All the gunner had to do was hold the sight on the target for a couple of seconds and fire, having set the enemy aircraft type on the dial. The computer would offset the guns automatically.