Description
WWII U.S. Navy Snap Switch Mk 3 Mod 0 Torpedo Director Illumination Rheostat
Item Overview
This WWII-era U.S. Navy Snap Switch Mk 3 Mod 0 is a sealed illumination switch and rheostat manufactured by Penn Electric Switch Co. of Goshen, Indiana. It provided BRIGHT, DIM, and OFF settings for illuminated optical equipment. This is an electrical fire-control component.
Identification and Features
The housing carries the official Navy Bureau of Ordnance designation “SNAP SWITCH MK-3 MOD-0.” Its four handle positions are marked OFF–DIM–OFF–BRIGHT, providing two OFF positions and two lighting levels. The correct handle marking is 669744-S-13. An inspection marking ending in “44” appears to indicate acceptance or inspection during 1944, but it should not be treated as a confirmed manufacturing date.
- Official designation: Snap Switch Mk 3 Mod 0
- Manufacturer: Penn Electric Switch Co.
- Manufacturer location: Goshen, Indiana
- Control positions: OFF–DIM–OFF–BRIGHT
- Lighting conditions: Bright, dim, and off
- Handle marking: 669744-S-13
- Probable inspection date: 1944
- Type: Sealed optical-illumination switch and rheostat
- Status: Non-explosive electrical component
How It Worked
Moving the handle operated a sliding electrical contact across an internal resistor coil. The BRIGHT position supplied stronger illumination, while DIM reduced the light level for nighttime viewing. Either OFF position opened the lighting circuit. A gasket and packing gland helped protect the internal contacts, resistor, and terminals from moisture and the exposed conditions found aboard a warship.
Torpedo Director Mk 27 Application
The strongest documented application is the crossline-illumination rheostat mounted on top of the U.S. Navy Torpedo Director Mk 27. It controlled the illuminated crosshairs inside the attached Telescope Mk 50. Navy manual OP 1586 describes the same BRIGHT, DIM, and OFF function, labels the rheostat in an installed view, and shows a cutaway matching this switch’s housing, gasket, packing gland, sliding contact, resistor coil, and terminals.
Weapon-System History
The Torpedo Director Mk 27 was a shipboard fire-control instrument used on U.S. Navy destroyers during World War II. Directors were commonly mounted near the signal bridge, where an operator tracked the target through Telescope Mk 50. The system used target and ship data to calculate torpedo course and gyro-angle orders, which were then transmitted to the torpedo-tube mounts. Adjustable crossline lighting helped the operator see the telescope reticle without creating excessive glare during nighttime operations.
Historical Background
The Snap Switch Mk 3 Mod 0 represents the specialized electrical equipment required by increasingly advanced naval fire-control systems during World War II. Sealed controls were important because directors operated in exposed areas affected by salt spray, rain, vibration, and changing light. Navy OP 1586, issued shortly after the war, preserved detailed operating and maintenance information for the Mk 27 director and its supporting equipment.
Identification Note
The switch’s essential identity and illumination function are well documented, and this type is shown on the Torpedo Director Mk 27. The meaning of marking 669744-S-13 remains unresolved. It may be a drawing, handle, or component identifier, but no digitized Navy catalog cross-reference has been located. Confirming that number would likely require original Bureau of Ordnance drawings or allowance lists.
Condition
This is an original military-surplus electrical component. It may show scratches, paint loss, discoloration, oxidation, dried preservative, worn markings, or other signs of age and storage. Internal electrical operation has not been stated and should not be assumed. This listing is for one Snap Switch Mk 3 Mod 0 only; the torpedo director, telescope, wiring, and other fire-control equipment are not included. Please check the pictures for the general condition of the item.
Ideal For
This uncommon component is well suited for collections and exhibits covering U.S. Navy torpedo fire control, destroyer equipment, and WWII naval electrical systems.
- World War II U.S. Navy collections
- Torpedo Director Mk 27 displays
- Telescope Mk 50 exhibits
- Naval fire-control research
- Historic electrical-component collections
- Military museums and educational displays
Approx length 5", Approx width 5", Approx height 4", Approx weight 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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