Product Overview: M28C Periscope Sight
NSN: 1240-00-706-0794
P/N: 8293432

(pictures are of M28C Periscope Sight)

Description and Data
(excerpted from the Field and Depot Maintenance Manual)

Description

1. The periscope sight M28C is a monocular-type optical sighting instrument of 1.5 power (Seiler offers a special 5 power version), with a 48 degree field of view. The sight serves as a member of the fire-control system in the M13 cupola on the full-tracked armored personnel carrier M59 and on the 4.2-inch full-tracked self-propelled mortar M84 to sight the cal. 50 heavy barrel Browning machinegun (TT) M2. The periscope sight M28C is also utilized as part of the machinegun fire-control system of the 90-mm gun full-tracked combat tank M48A2 to lay the cal. .50 machinegun (TT) M2 within the tank commander's cupola. When installed, the sight projects through the roof of the cupola and is located and supported by the periscope mount M104A1.
2. The eyepiece of the sight, which contains the eyelens, center lens and field lens, is fixed and remains stationary relative to the vehicle. The prism rotates the line of sight from 15 degrees depression to 60 degrees elevation in maintaining the line of sight parallel to the line of fire of the machinegun throughout the gun's full range. Connection from the gun to the sight is made through a quick-release sight link assembly, movement of which is transmitted to the prism through tape connected pulleys. The sight link assembly is not part of the periscope sight, but is issued as equipment with the sight.
3. Means for making azimuth boresighting adjustment is provided by azimuth adjustment pin at the mounting flange of the sight. Elevation adjustment is provided at the connecting arm to which the sight link assembly connects.
4. A rubber eyeshield, mounted over the sight's eyepiece, serves to protect the eyelens and prevent injury to the machine gunner. A dovetailed lamp bracket slot in the plate receives the lamp bracket of instrument light M50 which is furnished as equipment for periscope mount M104A1 in order that illumination of the sight's reticle during night operations may be accomplished.
5. An adjusting wrench is chained to the sight in order to provide the operator with a means of adjusting the azimuth adjusting pin while boresighting the installed sight.
6. The sight is sealed against the entrance of moisture to the optical system and is filled with dry nitrogen gas. Unit is also available with an optional heater.