DA Form 5424-R: Terrain Mortar Position Worksheet (LRA)

DA Form 5424-R: Terrain Mortar Position Worksheet (LRA) – DA Form 5424-R: Terrain Mortar Position/Special Corrections Worksheet (LRA) is a key U.S. Army form used by mortar platoons and sections for Terrain Mortar Positioning Corrections (TMPCs). It enables effective use of natural cover and concealment while maintaining accurate, standard sheaf fires on targets.

What Is DA Form 5424-R?

DA Form 5424-R (May 1985 edition, Locally Reproducible Artwork or LRA) is officially titled the Terrain Mortar Position/Special Corrections Worksheet. Mortar units employ it when mortars are positioned irregularly to exploit terrain features rather than in a standard linear formation. This positioning improves survivability against enemy detection and counterfire but requires firing corrections to achieve a proper sheaf.

The form computes position corrections (deflection, range, and time/fuze) for each mortar relative to the platoon center (base piece). These Terrain Mortar Positioning Corrections (TMPCs) compensate for lateral and depth displacements.

Key purposes include:

  • Achieving standard sheaves on targets without frequent adjustments.
  • Supporting dispersed positioning in defilade or vegetated areas.
  • Computing corrections for primary, left, and right sectors of fire.
  • Handling special missions, such as attitude fires.

Why Use Terrain Mortar Positioning?

In modern combat, mortar units face threats from enemy reconnaissance, artillery, and drones. Positioning mortars to fit terrain folds and vegetation (without regard to standard sheaf width) reduces signature. Standard sheaves require corrections when lateral spread exceeds the bursting diameter of HE rounds or depth varies significantly.

TMPC validity limits (approximate):

  • Primary sector: Typically ±200 mils left/right and ±2,000 meters over/short of center range.
  • Platoon dimensions: Up to 400m wide x 200m deep for six guns (smaller for fewer tubes).

Units compute separate TMPC sets for left, primary, and right sectors, plus range bands as needed.

How to Prepare and Use DA Form 5424-R?

Preparation involves these steps (detailed in FM 23-91 Appendix E and related publications):

  1. Determine Piece Displacement: Use hasty traverse, pacing, or estimation to measure each mortar’s position relative to the base piece (right/left and forward/behind the azimuth of lay).
  2. Plot on M16/M19 Plotting Board: Establish burst lines based on HE bursting diameter (e.g., ~40m for 81mm/120mm). Plot mortars and determine corrections to align each to a unique burst line.
  3. Fill the Worksheet:
    • Transfer Limits Block: Circle sector (L/P/R), note charge/elevation, referred deflections (L/C/R), and range bands (min/center/max).
    • Record piece displacements.
    • Compute lateral (deflection) corrections using mil conversion (100/R factor).
    • Compute range corrections (forward = minus, behind = plus).
    • Compute time/fuze corrections using tabular firing tables (TFT).
  4. Apply Corrections:
    • Squad leaders add/subtract deflection, adjust range (then re-extract charge/elevation), and modify fuze settings.
    • Or, FDC applies them before issuing commands.
    • Announce sector in fire commands (e.g., “LEFT SECTOR”) or “CANCEL TERRAIN CORRECTIONS.”

Hasty Positions: For rapid occupation, use a simplified method with baseline measurements for primary sector corrections, then compute full TMPCs as time allows.

Who Uses It?

  • Mortar Platoons/Sections (60mm, 81mm, 120mm) in Infantry, Stryker, and other units.
  • Fire Direction Centers (FDC) for computations.
  • Referenced in U.S. Army FM 7-90 / FM 23-91, MCWP 3-15.2 (USMC), and mortar gunnery manuals.

It remains relevant for training and operations emphasizing survivability and precision.

Download DA Form 5424-R

Official blank form: Available through Army publishing channels or unit resources (search AKO, APD, or your training management system for the latest reproducible copy).

Download DA Form 5424-R here – Ensure you use the current LRA version for local reproduction. Always verify with your unit SOP and current field manuals.

Training Tip: Practice with plotting boards and TFTs. Combine with registration points for even greater accuracy and ammunition savings.

Best Practices for U.S. Army Mortar Teams

  • Compute TMPCs before occupation when possible.
  • Establish SOPs for sector usage and announcements.
  • Recompute when displacement changes significantly or for new primary directions.
  • Integrate with MET data, registrations, and digital systems where available.
  • Train on hasty techniques for fluid battlefields.

Mastering DA Form 5424-R enhances mortar effectiveness, survivability, and mission success in contested environments. For full procedures, consult FM 23-91 (or successor publications) Appendix E on Terrain Mortar Positioning.