Description
U.S. Army 155AH2-ILLM485 Graphical Firing Scale Set for M109 155mm Howitzer
Item Overview
This U.S. Army 155AH2-ILLM485 graphical firing scale set was issued for fire-direction work with M485 illuminating projectiles fired by the M109 155mm self-propelled howitzer. The set contains two separately marked rules with transparent sliding cursors, stored together in a dedicated carrying case. Its February 1969 date, military stock number, and ammunition-specific markings identify it as a Vietnam-era artillery fire-control instrument rather than a general-purpose slide rule.
Identification and Features
The markings identify this as the M109-specific graphical firing scale for the 155mm M485 illuminating projectile. Rule 1 and Rule 2 contain printed ballistic scales for the weapon and ammunition combination, while the transparent cursors provide movable reference lines for reading firing data. The Charge 3 and Charge 7 markings identify the propelling-charge data shown on the visible rule faces.
- Official item: Scale, Graphical, Firing
- Scale designation: 155AH2-ILLM485
- Federal Stock Number: 1220-442-2444
- Modern NSN format: 1220-00-442-2444
- Weapon application: M109 155mm self-propelled howitzer
- Ammunition application: M485 illuminating projectile
- Components: Rule 1 and Rule 2
- Visible charge markings: Charge 3 and Charge 7
- Printed date: February 1969
- Carrying-case part number: 10549929
Historical Background
Graphical firing tables gave artillery fire-direction crews a compact way to obtain ballistic data without searching through large printed tables for every mission. When the M485 illuminating projectile entered service, earlier firing tables did not provide all the data needed for certain close-range self-illumination missions. The Army developed dedicated graphical firing scales matched to specific 155mm weapons and the M485 projectile. A March 1971 Army artillery publication identified this scale by designation and stock number as the version for the M109. The February 1969 rule date places this set within the period when these specialized illumination scales were being prepared for field use.
End-Item Application
The documented end-item application is the M109 155mm self-propelled howitzer. This set was used by fire-direction personnel supporting an M109 battery and was not an installed part of the howitzer. Its exact designation is important because the towed M114 155mm howitzer used a different M485 scale, designated 155Q4-ILLM485 under FSN 1220-133-6219. This distinction confirms that the present set was produced for the ballistic characteristics of the M109 weapon system.
How It Worked
Each rule carries logarithmic ballistic scales matched to the M109, the M485 projectile, and the listed propelling charge. The operator positioned a transparent cursor or hairline at the required range and read the related firing values from the printed scales. During an illumination mission, the fire-direction center combined these readings with the target location and standard firing corrections to determine the propelling charge, quadrant elevation, fuze setting, and intended height of burst. These calculations placed the projectile above the target area so its parachute-suspended illuminating candle could light the ground below.
Weapon-System Background
The M109 entered U.S. Army service during the early 1960s as a tracked, turreted 155mm self-propelled howitzer. The original vehicle mounted the 155mm M126 howitzer and gave armored and mechanized formations artillery that could move with them and deliver indirect fire from protected firing positions. Later M109 variants received longer-range weapons and other improvements, but the basic vehicle became one of the Army’s longest-serving self-propelled artillery designs. This scale was made for the original M109 ballistic system and should not be confused with scales prepared for other 155mm howitzers.
History of Use
Original-model M109 howitzers served during the Vietnam War, where self-propelled 155mm batteries provided fire support from bases and field positions. M485 illuminating projectiles were used during darkness and reduced visibility to light terrain for observation, target location, defensive fire, and adjustment of other artillery missions. Fire-direction crews worked with maps, firing charts, meteorological information, observer reports, and graphical firing tables to turn a fire request into commands for the gun crew. This February 1969 set comes from that manual, pre-digital period of artillery fire control.
Condition
This set includes the two separately marked graphical firing rules, their transparent sliding cursors, and the carrying case identified by part number 10549929. Visible markings include the 155AH2-ILLM485 designation, Charge 3 and Charge 7 data, Rule 1 and Rule 2 labels, the February 1969 date, and the military stock number. The listing is for the historical calculating instruments and carrying case shown in the inventory photographs.
Ideal For
This specialized scale set offers a documented connection to the M109 howitzer, M485 illuminating ammunition, and Vietnam-era field-artillery fire direction. Its exact weapon and ammunition designation makes it suitable for completing a technical display or adding a clearly identified analog computing instrument to a military collection.
- M109 howitzer displays and restorations
- Vietnam-era field-artillery collections
- M485 illuminating-projectile displays
- Military slide-rule and analog-computer collections
- Museum and educational fire-direction exhibits
Approx length 18", Approx width 5.5", Approx height 1", Approx weight 1.5lbs.
Pictures are stock images of our inventory. Unless otherwise noted, you will not be receiving the exact item shown in the pictures. The pictures are representative of the item’s general condition. The item you receive might be slightly better, or worse, condition than was shown in the pictures.
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