Description
Technical Manual (TM 9-1240-278-12) for M45/T151E1 Optical Bore Sight December 1959
Technical Manual (TM 9-1240-278-12) for M45/T151E1 Optical Bore Sight – December 1959
Item Overview
This December 1959 U.S. Army technical manual provides operator and organizational-maintenance instructions for the M45/T151E1 Optical Bore Sight.
The M45 was a portable optical instrument used to check the alignment of a mortar tube and its sight unit. It helped crews detect errors in elevation and deflection before firing.
This listing is for the technical manual only. It does not include an M45 bore sight, carrying case, mortar sight, tools, or other equipment.
Purpose of the M45 Optical Bore Sight
The M45 attached directly to the outside of a mortar tube with adjustable straps and clamps. Its machined V-shaped surfaces positioned the instrument in line with the tube.
The crew aimed the bore sight at a distant reference point and compared its view with the mortar’s regular sight unit. Any difference showed that the sight required adjustment. Correct alignment helped ensure that sight settings matched the actual direction and elevation of the mortar tube.
The M45 was used for inspection and calibration. It was not the sight normally used to aim the mortar during a firing mission.
Historical Background
The M45 was developed during the 1950s as the U.S. military improved its mortar sights and maintenance equipment. The T151E1 designation reflects the instrument’s development history before or during standardization as the M45.
Its adjustable mounting system allowed the basic bore-sight design to work with mortar tubes of different diameters. The M45 series later supported several generations of U.S. mortar equipment, including 81mm and 120mm systems.
Published in December 1959, this manual comes from the early Cold War period. It documents the original operating and maintenance practices for a bore-sighting system that remained useful for decades.
Manual Contents
TM 9-1240-278-12 covers the operation and unit-level care of the M45/T151E1. Subjects include:
- Description and operating principles
- Identification of major components
- Installation on a mortar tube
- Leveling and alignment procedures
- Checking elevation and deflection errors
- Operator inspections
- Preventive maintenance
- Cleaning and care
- Organizational troubleshooting
- Minor adjustments and repairs
- Storage and transportation
Identification
- Manual number: TM 9-1240-278-12
- Publication date: December 1959
- Covered equipment: M45/T151E1 Optical Bore Sight
- Manual type: Operator and organizational maintenance
- Equipment category: Mortar sight inspection and alignment equipment
- Primary purpose: Detecting elevation and deflection errors in a mortar sight
- Method of attachment: Adjustable straps and clamps around the mortar tube
Collector and Research Value
This manual is a valuable reference for understanding how U.S. mortar crews inspected and aligned their sighting equipment. Its December 1959 date also gives it strong value for early Cold War mortar and military-optics collections.
Ideal For
- M45 optical bore-sight owners
- U.S. mortar restoration projects
- Military-optics collections
- Cold War equipment displays
- Museum and educational exhibits
- Army technical-library collections
Approx length 8", Approx width 10", Approx height .15", Approx weight .2lbs.
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