Description
Technical Manual (TM 9-1240-277-35) for M42 Periscope July 1970 FSN 1240-864-2933
Technical Manual (TM 9-1240-277-35) for M42 Tank Periscope – July 1970
Item Overview
This July 1970 U.S. Army technical manual provides direct-support, general-support, and depot-maintenance instructions for the M42 Tank Periscope.
The M42 is identified by FSN 1240-864-2933, later written as NSN 1240-00-864-2933. Its military drawing and part number is 7645543.
The M42 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 a periscope, elbow telescope, telescope mount, or replacement parts.
Purpose of the M42 Periscope
The M42 was a unity-power armored periscope designed for use with the M118C Elbow Telescope. Together, these instruments provided the gun crew with an optical line of sight for aiming at visible targets.
The periscope shifted the viewing path around the howitzer’s gun and muzzle-brake area. This allowed the protected telescope inside the vehicle to see forward during direct-fire missions.
The M42 was part of the weapon’s fire-control system. It was not a general observation periscope for the driver or commander.
Historical Background
The M42 began as the XM42 during development of the M109 self-propelled howitzer. An earlier January 1963 edition of this manual covered the instrument under that experimental designation.
The M109 was standardized in 1963 and became one of the U.S. Army’s most important self-propelled artillery systems. The XM42 was standardized as the M42 and continued serving as part of the M109’s direct-fire optical equipment.
Published during the Vietnam War era, this July 1970 manual reflects the standardized M42 designation and the Army’s continued support of the M109 fire-control system.
Manual Contents
TM 9-1240-277-35 covers advanced maintenance of the M42 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
- 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: July 1970
- Covered equipment: M42 Tank Periscope
- Federal Stock Number: 1240-864-2933
- National Stock Number: 1240-00-864-2933
- Part and drawing number: 7645543
- Manual type: Direct-support, general-support, and depot maintenance
- Associated telescope: M118C Elbow Telescope
- End-item application: M109 155mm Self-Propelled Howitzer
Collector and Research Value
This manual is a valuable reference for M42 periscope repair, identification, and restoration. It also documents an important part of the M109 howitzer’s original direct-fire sighting system.
Ideal For
- M42 periscope restoration and research
- M109 howitzer restoration projects
- Military-optics collections
- Vietnam War artillery displays
- Museum and educational exhibits
- Army technical-library collections
Approx length 8", Approx width 10", Approx height .2", Approx weight .2lbs.
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