Description
Technical Manual (TM 9-1240-277-35) for XM42 Periscope January 1963
Technical Manual (TM 9-1240-277-35) for XM42 Periscope – January 1963
Item Overview
This January 1963 U.S. Army technical manual provides direct-support, general-support, and depot-maintenance instructions for the XM42 Tank Periscope.
The XM42 was the experimental designation for the optical instrument later standardized as the M42 Tank Periscope. It was part of the direct-fire sighting system used on the M109 155mm Self-Propelled Howitzer.
This listing is for the technical manual only. It does not include an XM42 or M42 periscope, elbow telescope, telescope mount, or replacement parts.
Purpose of the XM42 Periscope
The XM42 was a unity-power armored periscope designed for use with the M118C Elbow Telescope. Together, these instruments provided the gun crew with a direct-fire line of sight.
The periscope shifted the telescope’s viewing path around the howitzer’s gun and muzzle-brake area. This allowed the crew to aim at visible targets while the optical system remained protected inside the vehicle.
The XM42 was part of the weapon’s fire-control system. It was not one of the general observation periscopes used by the driver or commander.
Historical Background
The XM42 was developed during the creation of the M109, a tracked 155mm self-propelled howitzer designed to give Army artillery greater mobility and protection.
Published in January 1963, this manual predates the M109’s standardization later that year. Its use of the experimental “XM” designation reflects the system’s development period. The periscope was later standardized as the M42 and continued serving with M109-series howitzers.
The M109 became one of the most successful American self-propelled artillery systems. Updated versions remained in service for decades, while the M42 periscope and M118-series telescope formed part of its direct-fire optical equipment.
Manual Contents
TM 9-1240-277-35 covers advanced maintenance of the XM42 periscope. Subjects include:
- Description and operating principles
- Inspection and troubleshooting
- Disassembly and reassembly
- Cleaning and repair procedures
- Optical and mechanical components
- Window, prism, and housing assemblies
- Adjustment and optical alignment
- Sealing and moisture protection
- Final inspection and performance testing
- Required maintenance tools and equipment
These instructions were written for trained personnel responsible for returning damaged or unserviceable periscopes to military standards.
Identification
- Manual number: TM 9-1240-277-35
- Publication date: January 1963
- Covered equipment: XM42 Tank Periscope
- Later standardized designation: M42 Tank Periscope
- Manual type: Direct-support, general-support, and depot maintenance
- Equipment type: Armored artillery fire-control periscope
- Associated telescope: M118C Elbow Telescope
- End-item application: M109 155mm Self-Propelled Howitzer
Collector and Research Value
This manual documents the XM42 before its standardization as the M42. It is a useful reference for M109 restoration projects, military-optics research, and collections focused on early Cold War artillery development.
Ideal For
- XM42 and M42 periscope research
- M109 howitzer restoration projects
- Military-optics collections
- U.S. Army artillery displays
- Museum and educational exhibits
- Cold War technical-library collections
Approx length 8", Approx width 10", Approx height .2", Approx weight .2lbs.
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