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*FM 23-90/TO 11W2-5-13-21

FIELD MANUAL NO. 23-90 TECHNICAL ORDER NO. 11W2-5-13-21

HEADQUARTERS DEPARTMENT OF THE ARMY AND THE AIR FORCE WASHINGTON, DC, 1 March 2000

FM 23-90

MORTARS

Table of Contents

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PREFACE
CHAPTER 1		INTRODUCTION
Section	I	General Doctrine
		1-1.	Effective Mortar Fire
		1-2.	Mortar Positions
Section	II	Indirect Fire Team
		1-3.	Applications
		1-4.	Team Mission
Section	III	Safety Procedures
		1-5.	Duties of the Safety Officer and Supervisory Personnel
		1-6.	Ammunition Care and Handling
		1-7.	Field Storage of Ammunition
CHAPTER 2		SIGHTING AND FIRE CONTROL EQUIPMENT
Section	I	Compass, M2
		2-1.	Characteristics
		2-2.	Description
		2-3.	Use
Section	II	Aiming Circles, M2 and M2A2
		2-4.	Characteristics
		2-5.	Description
		2-6.	Use
		2-7.	Accessory Equipment
		2-8.	Setup and Leveling of Aiming Circle
		2-9.	Declination Constant
		2-10.	Orienting of the Instrument on Grid North to Measure Grid Azimuth to Objects
		2-11.	Measurement of Horizontal Angle Between Two Points
		2-12.	Orienting of the 0-3200 Line on a Given Grid Azimuth
		2-13.	Orienting of the 0-3200 Line on a Given Magnetic Azimuth
		2-14.	Verifying the Lay of the Platoon
		2-15.	Orienting by Orienting Angle
		2-16.	Disassembly of Aiming Circle
		2-17.	Care and Maintenance
Section	III	Sightunits
		2-18.	Sightunit, M53-Series
		2-19.	Operation of M53 Sightunit
		2-20.	Care and Maintenance of M53 Sightunit
		2-21.	Sightunit, M64-Series
		2-22.	Sightunit, M67
Section	IV	Boresights
		2-23.	Boresight, M45-Series
		2-24.	Boresight, M115
		2-25.	Principles of Operation
		2-26.	Installation
		2-27.	Sight Calibration
		2-28.	Boresight Method of Calibration
		2-29.	Calibration for Deflection Using the M2 Aiming Circle
Section	V	Other Equipment
		2-30.	Instrument Light, M53E1
		2-31.	Aiming Posts, M14 and M1A2
		2-32.	Aiming Post Lights, M58 and M59
Section	VI	Laying the Section
		2-33.	Reciprocal Laying
		2-34.	Reciprocal Laying on a Grid Azimuth
		2-35.	Reciprocal Laying on a Magnetic Azimuth
		2-36.	Reciprocal Laying Using the Orienting Angle
		2-37.	Reciprocal Laying Using the Mortar Sights
		2-38.	Reciprocal Laying Using the M2 Compass
		2-39.	Placing Out Aiming Posts
		2-40.	Alternate Method of Placing Out Aiming Posts
		2-41.	Correction for Displacement of Sight
Section	VII	Loading and Firing
		2-42.	Firing the Mortar
		2-43.	Target Engagement
		2-44.	Execution of Fire Commands
		2-45.	Arm-and-Hand Signals
		2-46.	Subsequent Fire Commands
		2-47.	Repeating and Correcting of Fire Commands
		2-48.	Reporting of Errors in Firing
		2-49.	Night Firing
CHAPTER 3		60-mm MORTAR, M224
Section	I	Squad and Section Organization and Duties
		3-1.	Organization
		3-2.	Duties
Section	II	Components
		3-3.	Tabulated Data
		3-4.	Cannon Assembly, M225
		3-5.	Baseplate, M7
		3-6.	Baseplate, M8
		3-7.	Bipod Assembly, M170
Section	III	Operation
		3-8.	Premount Checks
		3-9.	Mounting of the Mortar
		3-10.	Safety Checks Before Firing
		3-11.	Small Deflection and Elevation Changes
		3-12.	Large Deflection and Elevation Changes
		3-13.	Referring of the Sight and Realignment of Aiming Posts
		3-14.	Malfunctions
		3-15.	Removal of a Misfire
		3-16.	Dismounting and Carrying of the Mortar
Section	IV	Ammunition
		3-17.	Classification
		3-18.	Color Codes
		3-19.	Preparation of Ammunition
		3-20.	Types of Fuzes
		3-21.	Standard B Ammunition
		3-22.	Care and Handling
CHAPTER 4		81-mm MORTAR, M252
Section	I	Squad and Section Organization and Duties
		4-1.	Organization
		4-2.	Duties
Section	II	Components
		4-3.	Tabulated Data
		4-4.	Cannon Assembly, M253
		4-5.	Mount, M177
		4-6.	Baseplate, M3A1
Section	III	Operation
		4-7.	Premount Checks
		4-8.	Mounting of the Mortar
		4-9.	Safety Checks Before Firing
		4-10.	Small Deflection and Elevation Changes
		4-11.	Large Deflection and Elevation Changes
		4-12.	Referring of the Sight and Realignment of Aiming Posts Using M64 Sight
		4-13.	Malfunctions
		4-14.	Removal of a Misfire
		4-15.	Dismounting of the Mortar
Section	IV	Ammunition
		4-16.	Classification
		4-17.	Function
		4-18.	High-Explosive Ammunition
		4-19.	Red/White Phosphorus Ammunition
		4-20.	Illuminating Ammunition
		4-21.	Types of Fuzes
		4-22.	Characteristics of Proximity Fuzes
		4-23.	Fuze Wrench and Fuze Setter
		4-24.	Preparation of Ammunition
		4-25.	Care and Handling
CHAPTER 5		81-mm MORTAR, M29A1
Section	I	Squad and Section Organization and Duties
		5-1.	Organization
		5-2.	Duties
Section	II	Components
		5-3.	Tabulated Data
		5-4.	Cannon Assembly, M29A1
		5-5.	Bipod Assembly, M23A1
		5-6.	Baseplate, M3
Section	III	Operation
		5-7.	Premount Checks
		5-8.	Mounting of the Mortar
		5-9.	Safety Checks Before Firing
		5-10.	Small Deflection and Elevation Changes
		5-11.	Large Deflection and Elevation Changes
		5-12.	Referring of the Sight and Realignment of Aiming Posts Using M53 Sight
		5-13.	Malfunctions
		5-14.	Removal of a Misfire
		5-15.	Dismounting of the Mortar
Section	IV	Ammunition
		5-16.	Function
		5-17.	High-Explosive Ammunition
		5-18.	White Phosphorus Ammunition
		5-19.	White Phosphorus Ammunition
		5-20.	Types of Fuzes
		5-21.	Characteristics of Proximity Fuzes
		5-22.	Fuze Wrench and Fuze Setter
		5-23.	Preparation of Ammunition
		5-24.	Care and Handling
CHAPTER 6		4.2-INCH MORTAR, M30
Section	I	Squad and Section Organization and Duties
		6-1.	Organization
		6-2.	Duties
		6-3.	Section Drill and Section Leader Duties
Section	II	Components
		6-4.	Tabulated Data
		6-5.	Mortar Cannon, M30
		6-6.	Mortar Mount, M24A1
Section	III	Operation of Ground-Mounted Mortar
		6-7.	Mounting of the Mortar
		6-8.	Safety Checks Before Firing
		6-9.	Small Deflection Change
		6-10.	Large Deflection and Elevation Changes
		6-11.	Loading and Firing of M329A2 Round
		6-12.	Malfunctions
		6-13.	Removal of a Misfire
		6-14.	Dismounting of the Mortar
Section	IV	Mortar Carriers, M106, M106A1, and M106A2
		6-15.	Description
		6-16.	Tabulated Data
Section	V	Operation of Carrier-Mounted Mortar
		6-17.	Mortar and Vehicular Mount
		6-18.	Maintenance
		6-19.	Placement of Mortar Into Firing Position on Carrier
		6-20.	Laying for Deflection and Elevation
		6-21.	Removal of a Misfire (Carrier-Mounted)
		6-22.	Mounting of Mortar on Carrier From Ground-Mounted Position
		6-23.	Dismounting of Mortar From Carrier
		6-24.	Preparation for a March Order From Ground-Mounted Position
		6-25.	Safety Checks
		6-26.	Measurement of Minimum and Maximum Elevations
		6-27.	Squad Formations
		6-28.	Dismounted Mortar Squad
		6-29.	Reciprocally Laying the Mortar Carrier Section
Section	VI	Ammunition
		6-30.	Classification
		6-31.	Types of Fuzes
		6-32.	Preparation of Ammunition
		6-33.	Care and Handling
CHAPTER 7		120-mm MORTAR, M120
Section	I	Squad and Section Organization and Duties
		7-1.	Organization
		7-2.	Duties
Section	II	Components
		7-3.	Tabulated Data for the 120-mm Mortar, M120
		7-4.	Barrel Assembly, M298
		7-5.	Bipod Assembly, M191 (Carrier-/Ground-Mounted)
		7-6.	Bipod Assembly, M190 (Ground-Mounted)
		7-7.	Baseplate, M9
Section	III	Operations
		7-8.	Placing a Ground-Mounted 120-mm Mortar Into Action
		7-9.	Performing Safety Checks on a Ground-Mounted 120-mm Mortar
		7-10.	Performing Small Deflection and Elevation Changes on a Ground-Mounted 120-mm Mortar
		7-11.	Performing Large Deflection and Elevation Changes on a Ground-Mounted 120-mm Mortar
		7-12.	Malfunctions on a Ground-Mounted 120-mm Mortar
		7-13.	Performing Misfire Procedures on a Ground-Mounted 120-mm Mortar During Combat
		7-14.	Loading and Firing the Ground-Mounted 120-mm Mortar
		7-15.	Taking the 120-mm Mortar Out of Action
Section	IV	Mortar Carrier, M1064A3
		7-16.	Description
		7-17.	Tabulated Data for the M1064A3 Carrier
Section	V	Operation of a Carrier-Mounted 120-mm Mortar
		7-18.	Mortar and Vehicular Mount
		7-19.	Maintenance
		7-20.	Placing Carrier-Mounted 120-mm Mortar Into Action
		7-21.	Lay for Deflection and Elevation on a Carrier-Mounted 120-mm Mortar
		7-22.	Performing Misfire Procedures on a Carrier-Mounted 120-mm Mortar During Combat
		7-23.	Mounting of the Mortar From a Carrier to a Ground-Mounted Position
		7-24.	Taking the Mortar Out of Action (Ground-Mounted to M1064A3 Carrier-Mounted)
		7-25.	Performing Safety Checks on a Carrier-Mounted 120-mm Mortar
		7-26.	Reciprocally Laying the Mortar Carrier Section
Section	VI	Ammunition
		7-27.	Classification
		7-28.	Authorized Cartridges
		7-29.	Preparation for Firing
		7-30.	Loading and Firing
		7-31.	Unfired Cartridges
		7-32.	Care and Handling of Cartridges
		7-33.	Fuzes
		7-34.	Setting Fuzes
		7-35.	Resetting Fuzes
CHAPTER 8		FIRE WITHOUT A FIRE DIRECTION CENTER
Section	I	Fire Procedures
		8-1.	Advantages and Disadvantages
		8-2.	Firing Data
		8-3.	Observer Corrections
		8-4.	Initial Fire Commands
		8-5.	Fire Commands
		8-6.	Fire Control
		8-7.	Movement to Alternate and Supplementary Positions
		8-8.	Squad Conduct of Fire
		8-9.	Reference Line
		8-10.	Fire Adjustment
		8-11.	Squad Use of Illumination and Smoke
		8-12.	Attack of Wide Targets
		8-13.	Attack of Deep Targets
Section	II	Direct-Lay Method
		8-14.	Step 1: Initial Firing Data
		8-15.	Step 2: Referring the Sight
		8-16.	Step 3: Bracketing the Target
		8-17.	Step 4: Fire for Effect
Section	III	Direct-Alignment Method
		8-18.	Mortar Dismounted
		8-19.	Mortar Mounted
		8-20.	Natural Object Method
Section	IV	Adjustment of Range
		8-21.	Range Spottings
		8-22.	Miscellaneous Spottings
		8-23.	Bracketing Method
		8-24.	Creeping Method of Adjustment
		8-25.	Normal Fire Commands
		8-26.	Modified Fire Commands
		8-27.	Fire Control
		8-28.	Establishment of a Reference Line and Shifting From That Line
		8-29.	Ladder Method of Adjustment
CHAPTER 9		GUNNER'S EXAMINATION
Section	I	Preparatory Instruction
		9-1.	Methods of Instruction
		9-2.	Prior Training
		9-3.	Preparatory Exercises
		9-4.	Examining Board
		9-5.	Location and Date
		9-6.	Eligible Personnel
		9-7.	Qualification Scores
		9-8.	General Rules
Section	II	Gunner's Examination With Ground-Mounted Mortar
		9-9.	Subjects and Credits
		9-10.	Equipment
		9-11.	Organization
		9-12.	Procedure
		9-13.	Mounting of the Mortar
		9-14.	Small Deflection Change
		9-15.	Referring of the Sight and Realignment of Aiming Posts
		9-16.	Large Deflection and Elevation Changes
		9-17.	Reciprocal Laying
Section	III	Gunner's Examination With the Track-Mounted Mortar
		9-18.	Subjects and Credits
		9-19.	Equipment
		9-20.	Organization
		9-21.	Procedure
		9-22.	Placement of Mortar Into a Firing Position From Traveling Position
		9-23.	Small Deflection Change
		9-24.	Referring of the Sight and Realignment of Aiming Posts
		9-25.	Large Deflection and Elevation Changes
		9-26.	Reciprocal Laying
		9-27.	Support Squad
APPENDIX A		TRAINING DEVICES
APPENDIX B		MORTAR TRAINING STRATEGY
GLOSSARY
REFERENCES
AUTHENTICATION

DISTRIBUTION RESTRICTION: Approved for public release, distribution is unlimited.

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*This publication supersedes FM 23-90/TO 11W2-5-13-21, 19 September 1990; and TC 23-18, 24 August 1967.