Walk up to a fighter jet after a sortie and the smell hits you before anything else: warm kerosene. To most people, jet fuel is just jet fuel. To air forces and navies, it is a family of carefully specified liquids with names like JP-8, JP-5 and F-24, and the differences between them can decide whether a fire on a ship stays small or sinks it.

Here is what military jets actually burn, how it differs from the Jet A in an airliner, and why the aircraft on a carrier deck need a fuel of their own.

It all starts with kerosene

Almost every jet engine in the world, military or civil, runs on a kerosene-type fuel. The airliner you fly on holiday burns Jet A or Jet A-1, refined to tight international standards for things like freezing point, energy content and cleanliness. Military fuels start from the same base. What makes them military is what gets added, and in one case, how the fuel is refined.

Fuel matters to a fighter in ways it rarely matters to a car. It has to stay liquid at minus 40 degrees and colder at altitude, flow through tiny injectors, cool the engine oil and hydraulics before it is burned, and not catch fire too easily when a tank is punctured. Every military fuel is a compromise between those demands.

The US Navy on its Aviation Boatswain's Mates (Fuel), the sailors who store, test and pump JP-5 on carriers.

JP-8: the workhorse

JP-8, known in NATO as F-34, is essentially Jet A-1 with three additions: a fuel system icing inhibitor to stop water in the fuel freezing into ice crystals, a corrosion inhibitor that also improves lubricity, and an antistatic agent. Its flash point is 38 °C and it stays liquid down to around -47 °C.

The US Air Force used a different fuel, JP-4, for decades. JP-4 was a wide-cut blend of kerosene and gasoline-like fractions, easy to produce in wartime volumes but much more flammable. For better safety and combat survivability, the Air Force replaced it with JP-8, completing the switch by the end of 1995.

JP-8 also powers far more than aircraft. Under NATO's single-fuel concept, the same fuel goes into tanks, trucks, generators and even field heaters and stoves. The gas-turbine-powered M1 Abrams tank can run on it. Fewer fuel types means simpler logistics, which in wartime is worth a great deal.

JP-5: the carrier fuel

Aircraft carriers are a special case. A carrier stores millions of litres of fuel inside a steel hull, surrounded by weapons, with aircraft refuelled on a crowded deck. A fuel that gives off flammable vapour at warm temperatures is a serious hazard there.

So in 1952 the US Navy introduced JP-5, known in NATO as F-44 or AVCAT, for aviation carrier turbine fuel. Its defining feature is a minimum flash point of 60 °C, far higher than JP-8. Below that temperature it does not give off enough vapour to ignite easily, so a spill on a hot flight deck is much less likely to become a fire. Its freezing point is about -46 °C. The price is that it is more expensive to produce.

Military jet engines are generally cleared to run on several of these fuels, so a Navy jet can refuel with JP-8 or Jet A ashore. On board ship, though, the fuel in the tanks is JP-5.

F-24: back to the airport fuel

The latest twist is F-24. Rather than buying specially refined JP-8, US bases in the continental United States moved around 2014 to buying ordinary commercial Jet A and adding the military additive package on site. The result performs like JP-8 but is cheaper and easier to source, because it comes from the same supply chain as the airlines. Overseas, where Jet A-1 is the standard, the equivalent is simply Jet A-1 plus additives, which is JP-8 by another name.

So the next time you smell kerosene at an air show, it is worth knowing that the fighter in front of you is burning something very close to the fuel in your holiday flight, with just enough chemistry added to make it a weapon of war.

Battleship New Jersey explains JP-5 aviation fuel and why the Navy uses it at sea.

Fuel is also a logistics war in its own right, as this look at how the US military moves jet fuel in wartime shows.

Every gallon a fighter burns on a combat air patrol has to be refined, shipped, stored, tested and pumped first.

Sources: Wikipedia (JP-8, JP-5, Jet fuel), US Air Force, US Navy, MIL-DTL-83133, Battleship New Jersey