green plasticine with a distinctive smell of almonds. During World War II it was extensively used by the British Special Operations Executive (SOE) at Aston House for sabotage missions. It is also the explosive used in HESH anti-tank shells and was an essential factor in the devising of the Gammon grenade. Captured SOE-supplied Nobel 808 was the explosive used in the failed 20 July plot assassination attempt on Adolf Hitler in 1944. During and after World War II a number of new RDX-based explosives were developed, including Compositions C, C2, and eventually C3. Together with RDX, these incorporate various plasticizers to decrease sensitivity and make the composition plastic. The origin of the obsolete term "plastique" dates back to the Nobel 808 explosive introduced to the U.S. by the British in 1940. The samples of explosive brought to the U.S. by the Tizard Mission had already been packaged by the SOE ready for dropping via parachute container to the French Resistance and were therefore labeled in French, as Explosif Plastique. It is still referred to by this name in France and also by some Americans. Types Composition C The British used a plastic explosive during World War II as a demolition charge. The specific explosive, Composition C, was 88.3% RDX and 11.7% non-oily, non-explosive plasticizer. The material was plastic between , but was brittle at colder temperatures and gummy at higher temperatures. Composition C was superseded by Composition C2, which used a mixture of 80% RDX and 20% plasticizer. Composition C2 had a wider temperature range at which it remained plastic, from . Composition C2 was replaced by Composition C3, which was a mixture of 77% RDX and 23% explosive plasticizer. C3 was effective but proved to be too brittle in cold weather and was replaced with C4. There are three classes of C4, with varying amounts of RDX and polyisobutylene. Semtex List of plastic explosives Australia: PE4, PE4-MC Austria: KNAUERIT SPEZIAL Czech Republic: Semtex-1H (orange-colored), Semtex 1A (red-colored), Semtex 10 (also called Pl Np 10; black-colored), Pl Hx 30 (gray-colored) Finland: PENO France: Hexomax, Composition C-4 PLASTRITE (FORMEX P1, Pla Np 87) Germany: Sprengkörper DM12, P8301, Seismoplast 1 (Sprengmasse, formbar) Netherlands: Knaverit S1 (light orange-colored) Greece: C3, C4 India: PEK-1 Israel: Semtex Italy: T-4 Plastico Norway: NM91 (HMX), C4, DPX10 (PE8) Pakistan: PE-3A Poland: PMW, NITROLIT Russia: PVV-5A Plastic Explosive Slovakia: CHEMEX (Composition C-4 equivalent), TVAREX 4A, Pl Hx 30