OF-843A 120mm High-Explosive Fragmentation Mortar Bomb
1. Overview
The OF-843A is a Soviet/Russian 120mm high-explosive fragmentation (HE-Frag) mortar bomb representing an improved variant within the OF-843 ammunition family. This round has been a standard munition for Soviet and Russian 120mm mortar systems since the mid-20th century and remains one of the most widely proliferated mortar rounds in the world. The OF-843 series provides effective indirect fire capability against personnel and light materiel, and examples continue to be encountered in conflicts globally, including extensively during the ongoing Russia-Ukraine conflict.
2. Country/Bloc of Origin
- Country: Soviet Union / Russian Federation
- Development Period: Post-World War II era (original OF-843); OF-843A as improved variant
- Production: Multiple Soviet-era factories; continued production in Russia and successor states
- Proliferation: Extensive export to Warsaw Pact nations, Soviet client states, and global arms markets
The OF-843 family was developed to arm the 120-PM-43 mortar (and its successors), which itself evolved from the 120-PM-38 design that proved highly effective during World War II.
3. Ordnance Class
- Type: Mortar bomb (fin-stabilized, high-explosive fragmentation)
- Soviet/Russian Designation: Осколочно-фугасная мина (Fragmentation-High Explosive Mine)
- Primary Role: Anti-personnel, anti-materiel
- Delivery Method: Indirect fire from 120mm smooth-bore mortars including 120-PM-43, 2S12 Sani, 2B11, and compatible systems
4. Ordnance Family / Nomenclature
- Official Designation: OF-843A (ОФ-843А)
- GRAU Index: 53-ВФ-843А (when including full Soviet ordnance coding)
- Family Variants:
- OF-843 (Original variant; 12 fins, 6 gas check bands)
- OF-843A (Improved variant; 12 fins, 6 gas check bands)
- OF-843B (Further improved; 10 fins, 5 gas check bands)
- Associated Ammunition:
- S-843 Smoke round
- Z-843 Illumination round
- Various practice and training variants
Variant Identification
The OF-843 family variants can be distinguished by fin and gas check band configuration:
| Variant | Number of Fins | Gas Check Bands |
|---|---|---|
| OF-843 | 12 | 6 |
| OF-843A | 12 | 6 |
| OF-843B | 10 | 5 |
The OF-843A shares external configuration with the original OF-843 but incorporates internal improvements to reliability and manufacturing processes.
5. Hazards
Primary Hazards
- Blast: High-explosive detonation produces significant overpressure
- Fragmentation: Cast iron body designed for optimal fragmentation; produces numerous lethal fragments
- Mass Casualty Potential: Effective against groups of personnel in the open
Sensitivity Considerations
- Impact Sensitive: Point-detonating fuze (typically M-12) is designed for impact function
- Fuze Sensitivity: M-12 fuze in armed state is sensitive to handling and shock
- Thermal Stability: TD-50 or Amatol filler is relatively stable but degrades over time
Kill Radius and Danger Areas
- Effective Fragmentation Radius: Approximately 25-40 meters against exposed personnel
- Danger Zone: Fragments may travel several hundred meters; maintain appropriate safety distances
UXO Considerations
- Large quantities of OF-843 series remain as UXO in conflict zones globally
- Fuze may be armed upon impact failure; extremely hazardous
- Corrosion and age may increase sensitivity
- Body corrosion may expose explosive filler
Specific UXO Recognition
- Grey or olive drab body with Cyrillic markings
- Visible fin assembly at base
- M-12 or similar Soviet PD fuze at nose
- Gas check bands (grooves) visible on body circumference
6. Key Identification Features
Physical Characteristics
- Length: Approximately 674 mm (complete round)
- Diameter: 120mm body diameter
- Weight: Approximately 16 kg (35.2 lb) complete round
- Explosive Weight: 1.4-1.6 kg (varies by variant and manufacturer)
External Features
- Body: Cast iron construction optimized for fragmentation
- Shape: Ogive nose with cylindrical body tapering to tail boom
- Tail Boom: Contains primary propellant charge; multiple flash holes
- Fin Assembly: 12 fins (OF-843/843A) or 10 fins (OF-843B)
- Gas Check Bands: 6 grooves (OF-843/843A) or 5 grooves (OF-843B)
- Fuze Well Adapter: At nose to accept various Soviet PD fuzes
Color and Markings
- Body Color: Light grey or dark grey (may appear olive drab with age)
- Markings: Black Cyrillic stenciling
- Typical Markings Include:
- Lot number and year of manufacture
- Factory code
- Weight classification mark (+ or -)
- Explosive filler type designation
Fuze Recognition
- M-12 Fuze: Most common; cylindrical body with protective cap
- Setting: M-12 typically has SQ (“0”) and Delay (“3”) settings
7. Fuzing Mechanisms
Primary Fuze: M-12 Point Detonating Fuze
The M-12 (М-12) is the standard Soviet point-detonating fuze for the OF-843 series.
Fuze Characteristics
- Type: Mechanical, impact-initiated, nose-mounted
- Modes:
- “0” – Superquick (instantaneous detonation)
- “3” – Delay (brief penetration delay)
- Setting: Adjusted via rotating collar before firing
Arming Sequence
- Safety Pin: Removed before loading
- Setback: Upon firing, setback forces release internal safeties
- Spin: Although fin-stabilized (minimal spin), arming mechanisms complete
- Armed State: Fuze armed after safe separation distance from muzzle
Functioning
- Impact forces drive firing pin into detonator
- Detonator initiates booster charge
- Booster detonates main explosive filler
Alternative Fuzes
Other Soviet fuzes compatible with OF-843 series include:
- M-6 (basic PD fuze)
- M-12D (variant with different delay characteristics)
- Various modernized Russian fuzes
Anti-Handling Concerns
- Some fuzes incorporate anti-disturbance features
- Aged fuzes may be unpredictable
- Never assume any Soviet fuze is safe
8. History of Development and Use
Historical Background
The OF-843 family traces its lineage to World War II Soviet mortar development. The 120mm mortar caliber proved exceptionally effective during the Great Patriotic War, and the Soviets continued developing improved ammunition throughout the Cold War.
Development Timeline
- 1943: 120-PM-43 mortar enters service, replacing 120-PM-38
- Post-WWII: OF-843 ammunition standardized
- Cold War Era: OF-843A introduced with manufacturing improvements
- 1980s: OF-843B variant with modified fin configuration
- Present: Continued production in Russia and other states
Combat Employment
The OF-843 series has seen extensive combat use:
- Soviet-Afghan War (1979-1989)
- Yugoslav Wars (1991-2001)
- Chechen conflicts
- Syrian Civil War
- Russia-Ukraine conflict (2014-present)
- Numerous African and Middle Eastern conflicts
Proliferation
As standard Soviet ammunition, the OF-843 was exported globally:
- Warsaw Pact nations (all)
- Middle Eastern states (Egypt, Syria, Iraq, Libya)
- African nations
- Asian nations (Vietnam, North Korea, etc.)
- Various non-state actors through arms proliferation
Current Status
- Remains in active production in Russia
- Standard ammunition for Russian Army 120mm mortars
- Encountered extensively as UXO in Ukraine and other conflict zones
- Multiple nations continue to produce compatible variants
9. Technical Specifications
| Specification | Value |
|---|---|
| Caliber | 120mm |
| Complete Round Weight | ~16 kg (35.2 lb) |
| Body Material | Cast Iron |
| Explosive Filler | TD-50 (TNT/Dinitronaphthalene) or Amatol |
| Filler Weight | 1.4-1.6 kg |
| Standard Fuze | M-12 (PD, SQ/Delay) |
| Number of Fins | 12 (OF-843A); 10 (OF-843B) |
| Gas Check Bands | 6 (OF-843A); 5 (OF-843B) |
| Maximum Range | ~5,700-5,850 meters (system dependent) |
| Minimum Range | ~460 meters |
| Muzzle Velocity | ~272 m/s (892 ft/s) |
| Rate of Fire | 12-15 rounds/minute |
| Compatible Systems | 120-PM-43, 2S12 Sani, 2B11, and derivatives |
10. Frequently Asked Questions
Q: How can you distinguish the OF-843A from the OF-843B in the field? A: Count the fins and gas check bands (grooves on the body). The OF-843A has 12 fins and 6 gas check bands, while the OF-843B has 10 fins and 5 gas check bands. This is a reliable identification method even when markings are obscured by damage or corrosion. The OF-843B is the more modern variant encountered in recent conflicts.
Q: What does “TD-50” explosive filler mean? A: TD-50 is a Soviet explosive composition consisting of approximately 50% TNT (trotyl) and 50% dinitronaphthalene (DNN). It provides good fragmentation effects while being relatively stable and economical to produce. Some variants use Amatol (TNT and ammonium nitrate mixture) depending on manufacturer and production era.
Q: Why is the OF-843 body made of cast iron rather than steel? A: Cast iron is chosen specifically for its fragmentation characteristics. Cast iron fractures into numerous irregular fragments upon detonation, creating a more effective anti-personnel pattern than steel, which tends to produce fewer, larger fragments. This is a deliberate design choice optimizing lethality against personnel.
Q: Can the OF-843A be fired from U.S. M120 mortars? A: No, not safely. While both are 120mm caliber, the OF-843 series is designed for Soviet smooth-bore mortars with different chamber dimensions, propellant systems, and pressure tolerances. Attempting to fire Soviet ammunition in U.S. mortars (or vice versa) is extremely dangerous and prohibited.
Q: What is the M-12 fuze delay setting (“3”) used for? A: The delay setting provides a brief pause between impact and detonation, allowing the round to penetrate light cover, snow, or soft ground before exploding. This is useful when engaging troops in hasty fighting positions, buildings with light roofs, or when surface burst might be ineffective due to ground conditions.
Q: How does the OF-843 compare to the U.S. M933/M934? A: Both are effective 120mm HE rounds with similar purposes. Key differences include: the OF-843 uses cast iron (optimized for fragmentation) versus steel bodies; Soviet fuzing is mechanically simpler than the U.S. M734A1 multi-option fuze; U.S. rounds typically have longer maximum range due to propellant differences; and Soviet production emphasizes volume and cost-effectiveness over advanced features.
Q: What UXO hazards are specific to aged OF-843 ammunition? A: Aged OF-843 rounds may present: (1) Corroded fuzes that are unpredictable and may detonate with minimal disturbance, (2) Deteriorated explosive filler with reduced stability, (3) Body corrosion potentially exposing filler to moisture/contamination, (4) Propellant degradation affecting safety. Never approach, move, or disturb suspected UXO—report and evacuate.
Q: Why is the OF-843 series so widely encountered in global conflicts? A: The Soviet Union exported enormous quantities of 120mm mortar systems and ammunition globally during the Cold War, and production continues. The 120-PM-43 and its derivatives are among the most common heavy mortars in the world. Combined with long shelf life and ongoing production, OF-843 series rounds are ubiquitous in conflict zones from Ukraine to Africa to the Middle East.
This document is for educational and training purposes. All ordnance should be treated as dangerous until rendered safe by qualified EOD personnel. Report any suspected unexploded ordnance to appropriate military or law enforcement authorities.