As a result of the Marine Corps' desire to acquire a fixed power squad sniper scope system for the M-16 rifle to replace the substandard performing Colt 3x20 scope, in 1969 the Corps requested that Leatherwood Bros. build a small number of 2.5x three taper post reticle scope for evaluation. The resulting 2.5x USMC scope system consisted of a Realist made 1" black anodized tube mounted in standard blue finish Weaver made two screw rings.
The anodized detachable M-16 handle mount was subcontracted to pre-corporate formation Military Armament Corporation principals and manufactured by SIONICS Inc in April 1969. 12 units consisted of a two mount set with the addition of a single point XM-21 attachment. The first shipment of 12 non-serialized two mount scope systems were received Nov. 1969 by USMS Colonel Officer Codispoti, Commanding Officer, Hill 55 Da Nang I-CORPS RVN. Rings and mounts finished in Sandstron 9-A were also produced to evaluate combat durability. There scopes were not serialized and had a "USMC" marking on the left side of the turret housing.
Less than 20 of these scope units were produced for USMC evaluation with an additional production overrun of 20 units, placing the total manufacture of this scope at less than 40 units.
The USMC SOP "measure the mirage angle and divide by 4 = wind velocity" was developed using this scope system. Of the two mount systems only 6 units are known to have survived.
See Peter Senich's book "The Long Range War" p. 114 and Norman Chandler's book "Death from Afar" p. 58.