Composition B, almost universally called Comp B, is a military explosive made by combining roughly 60 percent RDX with about 39 percent TNT and a small fraction of wax. It has been one of the most heavily used explosive fills in conventional munitions since World War II, loaded into everything from mortar rounds and artillery shells to aerial bombs and landmines. Its longevity stems from a practical trick: RDX is a more powerful explosive than TNT, but it comes as a crystalline solid that cannot simply be melted and poured into a shell casing. TNT, on the other hand, melts at a conveniently low temperature. Blending the two gives Comp B the blast performance of RDX with the easy manufacturing of a melt-cast fill, and that combination kept it in front-line service for the better part of a century.
What Goes Into the Mix
The standard military-grade Composition B uses RDX and TNT in a nominal 60/40 ratio by weight, plus about one percent wax. RDX, sometimes called cyclonite, is the workhorse. It delivers most of the explosive energy. Its detonation velocity in pressed form sits well above that of TNT alone, which is why adding it raises the overall performance of the mixture. TNT serves as both a binder and a carrier: when heated past roughly 80 °C it becomes a liquid, and the RDX crystals can be stirred into that liquid the way sugar dissolves into warm water. Not all the RDX actually dissolves; much of it stays as suspended solid particles. The result, once cooled, is a dense, solid block of explosive that conforms to the interior shape of whatever casing it was poured into.
The wax component is easy to overlook, but it matters. Paraffin or similar waxes act as a desensitizer, reducing the chance that friction or impact during handling will set off the RDX. Research on how wax interacts with explosive crystals has shown that melted wax can infiltrate the surface of explosive particles and change the way those particles begin to decompose, lowering early decomposition energy while also slowing the overall reaction rate by absorbing some of the gaseous byproducts of decomposition.1Royal Society of Chemistry. The unusual effect of paraffin wax on the thermal decomposition of cyclotetramethylenetetranitramine In plain terms, that thin coating of wax makes the explosive less twitchy without meaningfully reducing its power when deliberately detonated.
How Comp B Is Manufactured
Comp B is a melt-cast explosive, and the phrase describes the process almost completely. TNT is heated until it liquefies. Granulated RDX and a small amount of wax are blended into the molten TNT, creating a slurry. That slurry is poured into the cavity of a munition casing and allowed to cool and solidify. The result is a monolithic charge that fills the casing with minimal voids or air pockets, which is important because trapped air can create hot spots that lead to unpredictable detonation behavior.
Thermal modeling of this process describes Comp B passing through several physical states as temperature rises: first the TNT binder melts, then some of the RDX crystals partially dissolve into the hot TNT, and finally the remaining RDX melts at higher temperatures if heating continues.2Combustion and Flame. Cookoff modeling of a melt cast explosive (Comp-B) Understanding these transitions matters for safety engineering: if a loaded shell is exposed to fire or sustained heat (a scenario called “cookoff”), the sequence in which its ingredients melt and begin to react determines whether the round detonates violently or burns comparatively gently. Modern cookoff models account for the way dissolved RDX in hot TNT and pressure buildup can accelerate reaction rates, helping weapons designers predict what happens when things go wrong in storage or transport.
Where Comp B Has Been Used
The list of munitions that have carried a Comp B fill is enormous. During World War II, it became the standard fill for many U.S. bombs, artillery projectiles, and anti-tank mines once domestic RDX production ramped up. After the war, Comp B filled mortar rounds (the 60 mm, 81 mm, and 120 mm families), shaped-charge warheads in anti-armor weapons, demolition charges, and various grenades. NATO allies adopted it widely, and it remained in service through the Korean War, the Vietnam War, and well into the conflicts of the early 21st century.
Its popularity in shaped charges is worth singling out. A shaped charge focuses explosive energy into a narrow jet that can punch through armor plate. The performance of that jet depends on the detonation pressure of the explosive behind the metal liner, and Comp B delivers substantially more pressure than plain TNT. Research into shaped-charge jet formation continues to use Comp B as a reference explosive in simulation and testing, evaluating how variables like liner geometry and explosive billet height affect penetration.3AIP Publishing. Formation of jets from hemispherical shaped charge liners That ongoing role as a benchmark reflects how deeply embedded Comp B is in the engineering knowledge base for military ordnance.
Sensitivity, Safety, and Handling
Comp B sits in a middle zone on the sensitivity spectrum. It is significantly less sensitive than pure RDX pressed into a charge, thanks to the TNT matrix and the wax coating on the crystals. You can drop a loaded Comp B round from a modest height without setting it off, and it generally needs a booster charge or detonator to initiate. At the same time, it is more sensitive than some newer formulations designed specifically for safety. The combination of being powerful enough for combat use while being handleable enough for field conditions is what made it the workhorse it became.
The gap test is one standard way to measure an explosive’s sensitivity to shock. In this test, a donor charge detonates on one side of an inert barrier of known thickness, and engineers observe whether the shock wave transmitted through the barrier is strong enough to set off the test sample on the other side. Comp B’s behavior in gap tests has been studied extensively, including modeling work on how a precursor shock wave can actually desensitize the explosive ahead of the main detonation wave, a counterintuitive effect that influences how Comp B performs in complex detonation scenarios.
For everyday handling, the primary risk is not accidental detonation but rather long-term chemical instability. TNT can exude from the mixture over time, forming crystals on the surface of a round, and old Comp B fills can develop internal cracks as the material ages. Both conditions potentially create sensitivity hazards in munitions that have sat in storage for decades.
Environmental Contamination
Wherever Comp B has been manufactured, tested, or used in combat, its chemical ingredients end up in the soil and water. Both TNT and RDX are persistent pollutants. TNT gives soil a yellowish stain and is toxic to many organisms. RDX moves more easily through groundwater and has been detected in drinking-water wells near former military ranges. Soil contamination from these compounds poses ongoing challenges, and a growing body of research focuses on bioremediation strategies to break them down, including using certain fungi, plants, and microbial communities to metabolize the explosive residues.4PubMed Central. Review of Explosive Contamination and Bioremediation: Insights from Microbial and Bio-Omic Approaches
The scale of contamination is not trivial. Military training ranges fire thousands of rounds per year, and a fraction of those fail to detonate, leaving intact or partially detonated Comp B charges sitting in the soil. Live-fire ranges at installations across North America, Europe, and elsewhere have measurable RDX and TNT plumes in their groundwater. Cleanup is expensive, slow, and often incomplete, which is one reason the push toward replacement explosives is partly motivated by environmental goals rather than purely by safety concerns.
Underwater Munitions and Marine Toxicity
Millions of tons of conventional munitions were dumped at sea after World War II and the Korean War, and large quantities of unexploded ordnance lie on the seafloor in former combat zones. Many of those munitions contain Comp B. As casings corrode, the explosive fill gradually dissolves into the surrounding water and sediment, raising questions about the ecological impact.
Research simulating worst-case marine exposure to Comp B found that dissolved explosive concentrations in the water column above the fragments generally stayed below known toxicity thresholds. However, concentrations in the pore water of sediment immediately adjacent to the fragments were high enough to be hazardous, limiting dangerous exposure to very localized scales around each munition.5PubMed. Fate and effects of Composition B in multispecies marine exposures In practical terms, a corroding Comp B round on the ocean floor creates a small toxic halo in the sediment around it, but the open water a short distance away remains relatively unaffected. The risk is primarily to bottom-dwelling organisms that live in or on the sediment directly next to a munition, not to fish swimming overhead or to the broader marine ecosystem.
That localized pattern does not mean the problem is negligible. In areas with dense concentrations of dumped ordnance, those small toxic halos can overlap, and organisms that burrow through contaminated sediment face chronic exposure. Efforts to map and sometimes remove underwater munitions are ongoing in the Baltic Sea, the Adriatic, and off the coasts of the United States and Japan.
Detecting Comp B Residues
Whether the goal is security screening, forensic investigation after a bombing, or environmental monitoring, identifying traces of Comp B and its ingredients is an active area of research. Two recent advances illustrate how detection technology is evolving.
For standoff detection, where you want to find explosive traces from a safe distance, a laser-based technique called laser fragmentation combined with laser-induced fluorescence has shown promise. In testing, this method detected trace amounts of several nitro-group explosives, including Comp B, on surfaces at distances of several meters, identifying concentrations as low as about one microgram per square centimeter.6Photonics. Remote Detection and Visualization of Surface Traces of Nitro-Group-Containing Explosives A scanning detector based on this principle could sweep a suspicious vehicle or package without anyone having to touch it.
For post-blast forensics, the challenge is different: the explosive has already detonated, and investigators need to figure out what it was from the residue. Recent work using a single-particle mass spectrometer to analyze aerosol particles collected during controlled detonations found that different explosives leave distinct chemical fingerprints. Comp B, for instance, produced strong polycyclic aromatic hydrocarbon signals along with inorganic ions from stabilizers and primers, a pattern distinguishable from other common military explosives like PETN or HNS.7PubMed. Characterization of explosives in a controlled blast chamber using single-particle mass spectrometer for post-blast particle analysis Being able to identify the specific explosive used in an attack helps forensic teams trace the munition back to its source.
The Push Toward Insensitive Replacements
For all its effectiveness, Comp B has a vulnerability that modern military logistics finds increasingly unacceptable: it can detonate sympathetically. If one round in an ammunition storage area goes off due to fire or enemy attack, the blast can set off neighboring rounds loaded with Comp B, turning a single incident into a catastrophic chain reaction. This vulnerability has driven the U.S. Army and allied militaries toward “insensitive munitions,” explosive fills designed to resist accidental detonation while still matching the blast performance of legacy materials.
The leading replacement for Comp B in mortar rounds is a formulation called IMX-104, developed and produced at the Holston Army Ammunition Plant. A companion formulation, IMX-101, targets TNT-only fills in artillery rounds.8Propellants, Explosives, Pyrotechnics. A Review on IMX‐101 and IMX‐104 Melt‐Cast Explosives: Insensitive Formulations for the Next‐Generation Munition Systems Both are melt-cast explosives, meaning they can be manufactured on the same production lines that currently pour Comp B, which keeps conversion costs manageable. The Army has selected IMX-104 specifically as a common low-cost replacement for Composition B in indirect fire weapons like mortar systems.9PubMed. Analysis of munitions constituents in IMX formulations by HPLC and HPLC-MS
The transition is not instantaneous. Enormous stockpiles of Comp B-loaded munitions still exist worldwide, and many nations that lack the infrastructure to produce IMX-104 will continue using Comp B for years or decades. Qualification testing for insensitive munitions is slow and methodical: every new fill must prove it matches or exceeds the old fill’s performance across blast, fragmentation, and shaped-charge metrics, while also passing a battery of insensitive munitions tests including bullet impact, fragment impact, slow cookoff, fast cookoff, and sympathetic detonation. IMX-104 has cleared many of these hurdles, but full fleet transition takes time.
Why Comp B Stayed in Service So Long
Part of the answer is pure inertia. Military supply chains are conservative by design, and changing an explosive fill means requalifying every munition that uses it, rewriting manufacturing procedures, retraining production workers, and updating logistics databases across dozens of countries. When the existing fill works and troops are familiar with it, the institutional resistance to change is substantial.
But Comp B also genuinely earned its longevity on technical merit. Its performance sits in a sweet spot: powerful enough for anti-armor and demolition work, castable at low temperatures with simple equipment, stable enough for tropical and arctic storage, and compatible with a vast range of fuze and booster designs developed over decades. Few other explosives check all those boxes simultaneously. Pure RDX is more powerful but cannot be melt-cast. Plastic explosives like C-4 are convenient for demolition but impractical for filling artillery shells on a production line. PETN-based compositions are more sensitive to impact. Comp B threaded the needle for a remarkably long time.
The ongoing shift to insensitive munitions is less a verdict that Comp B was a bad explosive and more a recognition that the threat environment changed. Modern military operations increasingly involve transporting ammunition by air, staging it in forward positions close to the front, and storing it in conditions where fire or enemy indirect fire can reach it. Under those conditions, the risk that one ignition event cascades into a magazine explosion is too high for a fill as shock-sensitive as Comp B. The replacement formulations trade a modest amount of raw blast output for a dramatic improvement in resistance to accidental initiation, and in the current operational calculus that trade is worth making.