Original Item. Only One Available. This is a very nice original U.S. M4 Collimator Sight, a precision aiming instrument used with the American 60mm M2 and 81mm M1 mortars during WWII. It is accompanied by its correct M14 leather carrying case.

The sight is constructed from black-finished metal and retains its distinctive rectangular collimator housing, auxiliary open sight, graduated elevation and deflection adjustment knobs, spirit levels, and dovetailed mounting bracket. The body bears the model designation SIGHT, M4 and serial number 142728. The adjustable scales retain their white-filled graduations, including the L and R markings used for lateral deflection.

The accompanying brown leather M14 carrying case is made from heavy stitched leather, with a reinforced lid, front closure strap, and metal suspension rings. The front is clearly stamped:

D29377
CASE, CARRYING
M14

The interior retains a worn manufacturer's stamp, with portions of the lettering still discernible, although the full inscription is difficult to establish.

Condition is very good overall, with expected age, handling, and storage wear. The sight retains much of its black finish, with scattered scratches, minor paint loss, and wear around the adjustment knobs and exposed edges. The graduated scales remain legible, and the principal optical and leveling components are present. The leather case remains structurally sound, showing surface scuffing, creasing, and wear along the edges and corners. Its closure strap and suspension hardware are retained, while the shoulder strap is absent. The sight's optical alignment, mechanical accuracy, and functionality have not been tested.

Historical Context

The M4 Collimator Sight was an important component of American infantry mortar equipment during WWII. Standardized for use with both the 60mm M2 and 81mm M1 mortars, it allowed mortar crews to establish the elevation and direction required for accurate high-angle fire.

The 60mm M2 mortar was generally assigned to infantry rifle companies, providing immediate fire support against enemy positions, machine-gun emplacements, and concentrations of personnel. The heavier 81mm M1 was typically employed by battalion heavy weapons companies, offering greater range and explosive power. Both weapons were particularly valuable for engaging targets concealed behind terrain, buildings, or other obstacles, where direct fire from conventional infantry weapons was often impractical.

The M4 was designed primarily for laying mortars in indirect fire, where the target was not necessarily visible from the weapon's position. Rather than aiming directly at the target, the gunner used a designated reference point, usually an aiming stake placed at a suitable distance from the mortar. The collimator presented a vertical reference line within its viewing field, which the gunner aligned with the aiming point while adjusting the mortar's elevation and direction.

The sight incorporated separate adjustment mechanisms for elevation and horizontal deflection. Elevation was measured in degrees, with a working range of 40° to 90° and a micrometer graduated in quarter-degree increments. Horizontal deflection was measured in mils, with adjustments extending 150 mils to either side of the normal setting. These measurements allowed the crew to apply firing data and make controlled directional corrections as necessary.

Two spirit levels, arranged for longitudinal and cross-level adjustment, helped the gunner maintain the proper alignment of the instrument. This was especially important when firing from uneven terrain, where an improperly leveled mortar could produce errors in direction or elevation. The collimator housing could also be adjusted independently in elevation to bring the aiming point into view without changing the mortar's established elevation setting.

An auxiliary open sight was incorporated beneath the collimator. In addition to providing a secondary vertical reference, it could assist the crew in assessing clearance over nearby obstacles, an important consideration when placing mortars in confined or concealed firing positions.

The M4 was designed to be detached from the mortar during transportation and protected in its fitted carrying case. The M14 case helped safeguard the instrument against impacts and environmental exposure, which could affect the alignment of its optical and mechanical components. Wartime operating procedures also emphasized careful handling and protection from moisture, with adjustments to the instrument's internal alignment reserved for qualified ordnance personnel.

Throughout WWII, American 60mm and 81mm mortar crews relied on these sighting systems to deliver infantry fire support under widely varying field conditions. The M4's optical reference, graduated adjustments, and leveling mechanisms formed an essential part of the gunner's equipment, allowing mortar fire to be directed and corrected with precision.