Description
U.S. Army M148 Telescope Mount for M120 Sight and M139 20mm Gun, NSN 1240-00-930-4258
Item Overview
This U.S. Army M148 Telescope Mount was the mechanical quick-release and boresight-adjustment mount for the M120 6× day telescope. It was installed beside the M139 20mm automatic cannon in the XM27/M27 powered cupola of the M114A1E1 armored command and reconnaissance carrier. The M120 telescope is not included.
Identification and Features
The original carton markings, serial number, stock number, and technical records provide a firm identification for this Vietnam War-era fire-control component.
- Official designation: Telescope Mount M148
- Original Federal Stock Number: 1240-930-4258
- Later National Stock Number: 1240-00-930-4258
- Drawing/design-control number: 10543453
- Supported telescope: M120 6× straight telescope
- Weapon: M139 20mm automatic cannon
- Cupola: XM27/M27 powered cupola
- Vehicle: M114A1E1 armored command and reconnaissance carrier
- Individual serial number: 2426
- Contract: DAAA25-69-C-0532
- Package marking: A-10/69
- Prime contractor: Chrysler Corporation, Dayton, Ohio
- Status: Inert mechanical sight-mount assembly
- Not included: M120 optical telescope
How the M148 Mount Worked
The mount’s silver stepped end received the dovetail base of the M120 telescope. Moving the long clamping lever locked the telescope firmly into place or released it for removal. Separate azimuth and elevation adjustments allowed an armorer or crew member to align the telescope’s line of sight with the M139 cannon. The mount provided approximately 20 mils of adjustment in either direction for both azimuth and elevation.
M120 Direct-Fire Sight
The M120 was a 6× straight telescope used as the primary daylight sight for the M139 cannon. The M148 mount, M120 telescope, and M52E1 instrument light formed a direct-fire sighting system. The magnified view helped the gunner identify and engage targets at greater distances than the cupola’s basic lower sight. The telescope could be removed quickly when it was not required or when maintenance was needed.
M139 Cannon and M27 Cupola
The M139 was a rapid-fire 20mm revolver cannon installed in the powered M27 cupola. The cupola allowed the vehicle commander to control elevation and full-circle traverse from inside the vehicle. Army training guidance listed the weapon for use against lightly armored vehicles at ranges up to about 1,000 meters and soft targets or personnel at distances up to about 1,800 meters. The M120 telescope and M148 mount provided the accurate daylight aiming needed for those engagements.
Vehicle History and Use
The M114 was developed during the early 1960s as a lightweight tracked vehicle for battlefield reconnaissance and command duties. The vehicle family served with U.S. forces in Vietnam. The improved M114A1E1 received the XM27/M27 powered cupola and M139 cannon to provide greater firepower than earlier machine-gun installations. This version later became commonly known as the M114A2, although contemporary Army manuals normally identify it as the M114A1E1.
Training and Boresighting
Army crews used the M148 adjustments to zero the M120 telescope with the cannon before firing. Training tables directed crews to engage stationary panels at approximately 1,000 meters using single shots and controlled fire. The telescope mount had to remain secure and properly aligned so the sight picture matched the cannon’s point of impact during training and field use.
Contract and Packaging History
Contract DAAA25-69-C-0532 was recorded in May 1969 as a $69,000 military procurement action with Chrysler Corporation of Dayton, Ohio, as the prime contractor. Estimated completion was February 1970. Chrysler’s contract role does not prove that it fabricated every individual part. The marking A-10/69 most likely indicates Level-A military packaging completed in October 1969 rather than the exact manufacturing date. Number 10543453 served as the M148 design-control number and its packaging-data-sheet number.
Condition
This is a military-surplus M148 telescope mount without the M120 optical telescope. It may show scratches, finish wear, oxidation, dried preservative, discoloration, handling marks, or other signs of age and storage. The mechanical lever and adjustment parts have not been tested for serviceability. Please check the pictures for the general condition of the item.
Ideal For
This original sighting-system component is well suited for displays and collections covering Vietnam War armored vehicles, U.S. Army fire-control equipment, and vehicle-mounted automatic cannons.
- M114A1E1 and M114A2 restoration projects
- XM27 and M27 powered-cupola displays
- M139 20mm cannon collections
- M120 telescope and sighting-system exhibits
- Vietnam War armored-vehicle collections
- Military museums and educational displays
Approx length ", Approx width ", Approx height ", 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.
Please visit our page about order lead times here: Order Lead Times