Description
U.S. Military M78 Carrying Case for M34-Series Sight Units – P/N 7693845
Item Overview
This U.S. military M78 carrying case was made to transport and protect an M34-series sight unit and its related equipment. Its fitted interior held the sight, M42 instrument light, four dry-cell batteries, and electrical cable in assigned positions. The faint exterior marking reads “CASE, CARRYING, M78,” followed by part number 7693845. That part number cross-references to NSN 1240-00-769-3845, Case, Optical Instrument, with the M34A2 sight unit identified as the equipment accommodated. This listing is for the empty carrying case with its remaining internal fittings and straps.
Identification and Features
The M78 is a purpose-built military optical-instrument case rather than a general storage box. Its internal stand secured the sight in the same manner as the weapon’s sight bracket, while separate clips and compartments held the light, batteries, and cable. The instruction chart inside the lid gives the instrument settings needed for proper stowage and also lists T13E5 elevation quadrants and T148E1 telescope mounts.
- Official marking: CASE, CARRYING, M78
- Part number: 7693845
- NSN: 1240-00-769-3845
- Catalog name: Case, Optical Instrument
- Cataloged equipment: M34A2 sight unit
- Original M34 equipment: M42 instrument light, four batteries, and cable
- Additional lid references: T13E5 and T148E1
- Construction: Fitted military carrying case
Historical Background
The M78 case was documented with the M34 sight unit in the March 1949 edition of TM 9-314. The manual shows the case as part of the sighting equipment for the 75mm M20 recoilless rifle and explains how its interior fittings organized the sight and night-lighting equipment. Later supply records retained part number 7693845 and placed the case under the standardized federal stock system as an optical-instrument case for the M34A2. The case therefore followed the M34 sight family as that equipment continued into postwar mortar and supporting-weapon service.
End-Item Applications
The original application documented in TM 9-314 is the M34 sight used with the 75mm M20 recoilless rifle. Later M34-series configurations served with the M29 and M29A1 81mm mortars and the M30 4.2-inch mortar. FM 23-85 also confirms that the M34A2 could be used to lay the 60mm M19 mortar for elevation and deflection. The lid chart adds settings for the T13E5 elevation quadrant and T148E1 telescope mount. Those instruments were used in the T127E1 and T128E1 sight units supplied for the 4.5-inch T66 and T66E2 multiple rocket launchers. These markings document the case’s compatibility with more than one field sight configuration.
How It Worked
The M34 sight unit combined a telescope mount with an elbow telescope for setting elevation and azimuth or deflection. A gunner entered the required angles on the sight’s scales and micrometers, leveled the instrument, and aligned its reticle with an aiming point. The M42 instrument light illuminated the reticle for night operation. Inside the M78 case, the sight locked onto a fitted stand, while clips retained the light and batteries and the cable remained stored for connection after the weapon was emplaced. The lid chart instructed the crew where to position adjustable instruments before closing the case.
Weapon-System Background
The M34 sight family supported several crew-served weapons with different battlefield roles. The M20 was a portable 75mm recoilless rifle used for direct fire and limited indirect fire. The M19 was a lightweight 60mm mortar, while the M29 and M29A1 were 81mm infantry mortars used for longer-range supporting fire. The rifled 4.2-inch M30 was a heavier mortar designed to deliver high-angle fire. The T66 and T66E2 were experimental 4.5-inch multiple rocket launchers developed during World War II. All required portable sighting equipment that could be carried safely between firing positions.
History of Use
The M78 case first appears with the M34 sight in early postwar Army documentation. The M20 recoilless rifle saw extensive service during the Korean War, while later M34-series sights remained associated with U.S. mortar equipment into the Vietnam era. At the firing position, crews removed the sight from its case, mounted it on the weapon, and used assigned elevation and deflection data to lay the weapon. After the mission, the case protected the sight’s optics, levels, scales, and adjustment mechanisms during movement and storage. The continued appearance of M34-series equipment in later manuals shows the long service life of this sighting system.
Ideal For
This M78 case is a documented accessory for several important U.S. recoilless-rifle, mortar, and rocket-launcher sighting systems. Its original fittings, identification, and stowage chart make it useful for completing an optical-equipment display or restoring the supporting equipment carried with an M34-series sight.
- M34 and M34A2 sight displays
- 75mm M20 recoilless-rifle collections
- M19, M29, M29A1, and M30 mortar displays
- T66 and T66E2 rocket-launcher exhibits
- Korean War and Vietnam-era collections
- Military optics and fire-control restorations
Approx length 10", Approx width 7", Approx height 5", Approx weight 7.3lbs.
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