Description
WWII Sperry Type K-3 B-17 Upper-Turret Automatic Computing Gunsight, P/N 644853, S/N 111684
The WWII Sperry Type K-3 B-17 Upper-Turret Automatic Computing Gunsight, plate-marked part number 644853 and serial number 111684, is the local-control fire-control sight used with the Sperry A-1, A-1A, and A-1B upper turrets installed on the B-17 Flying Fortress. These turrets paired the sight with two .50-caliber machine guns.
The National Cash Register Company of Dayton, Ohio manufactured this example to a Sperry Gyroscope Company design. This is the K-3 sight assembly, not a complete turret or the remote central fire-control sight associated with the B-29.
This example was manufactured by The National Cash Register Company in Dayton, Ohio, under license from Sperry Gyroscope Company, Inc. It was made for the Sperry A-1, A-1A and A-1B upper turrets, which carried two .50-caliber M2 Browning aircraft machine guns.
Historical Significance
The K-3 belongs to the wartime development of powered aircraft turrets and compact mechanical analog fire-control computers. Rather than serving as a simple fixed reticle, it combined an optical sight, range-finding inputs, and a mechanical computing mechanism in one unit for the B-17's locally controlled upper turret.
The identification plate does not state a manufacture date. However, an Imperial War Museums K-3, serial number 111738, carries the same part number, contract, and purchase order and is dated 1945. Because that example is only 54 serial numbers later than serial number 111684, 1945 production is strongly supported but not plate-proven for this sight.
K-3 Upper-Turret and K-4 Lower-Turret Applications
The Type K-3 was configured for the upper locally controlled Sperry turret. The related Type K-4 was arranged for the lower ball turret, with flexible-shaft input connections positioned for the inverted installation and some lettering inverted for the gunner. That distinction makes this K-3 the upper-turret model rather than a K-4 lower-turret sight.
What This Item Is and Does
The K-3 is an automatic computing optical gunsight. The gunner entered the target aircraft's known wingspan and adjusted range until the reticle framed the target. Flexible-shaft connections supplied turret azimuth and gun-elevation inputs to the sight.
Inside the unit, cams and variable-speed mechanisms calculated prediction and ballistic corrections. Those corrections shifted the optical line of sight so the sight presented a corrected aiming point while the sight cradle moved with the guns.
Key Features
- Official plate nomenclature: Automatic Computing Sight, Turret (Upper), Local Control
- Type: K-3
- Part number: 644853
- Serial number: 111684
- Manufacturer: The National Cash Register Company, Dayton, Ohio
- Design authority: Sperry Gyroscope Company
- Contract: W33-038-AC-7564
- Purchase order: (33-038) 45-7200P
- Verified turret applications: Sperry A-1, A-1A, and A-1B upper turrets
- Aircraft application: B-17 Flying Fortress
- System role: Local-control computing sight for the upper turret's twin .50-caliber machine guns
- Manual-specified electrical supply: 24 to 27.5 volts DC
Why This Item Matters
This K-3 is a plate-identified example of the mechanical analog computing technology used in World War II aircraft fire control. Its exact part number, serial number, manufacturer, contract, and purchase-order markings make it useful for B-17 turret research, restoration reference, and technical display.
The surviving sight also illustrates the division between local turret control and the later remote fire-control systems found on other bomber designs.
About This Item
The offered Sperry Type K-3 Automatic Computing Gunsight is marked P/N 644853 and S/N 111684. Its plate identifies The National Cash Register Company, Dayton, Ohio, as manufacturer and records contract W33-038-AC-7564 and purchase order (33-038) 45-7200P.
This sight was used with the Sperry A-1, A-1A, and A-1B locally controlled upper turrets on the B-17 Flying Fortress, where it provided the optical and computing function for the turret's twin .50-caliber machine guns. The offered item is the K-3 sight assembly only, not a complete turret.
All items are opened from the original packaging to verify its condition before shipment. If your prefer to receive an item in its original, unopened packaging, please indicate your request in the order comments at checkout. Please Note: If you request an item in its original, unopened packaging, we are unable to verify the item's condition prior to shipment.
Ideal For
Ideal For
- B-17 Flying Fortress restoration projects
- Sperry A-1, A-1A and A-1B upper-turret displays
- World War II aviation collections
- U.S. Army Air Forces armament exhibits
- Military aircraft fire-control collections
- Mechanical and analog-computer displays
- Sperry Gyroscope Company collections
- National Cash Register Company industrial-history displays
- Military museums and educational exhibits
- Twin .50-caliber aircraft-turret displays
Approx length 14", Approx width 14", Approx height 11", Approx weight 25 lbs.
Pictures are stock images of our inventory. Unless otherwise noted, you will not be receiving the exact item shown in the pictures. The pictures are representative of the item's general condition. The item you receive might be slightly better, or worse, condition than was shown in the pictures.
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