Ernst Eger of United States Rubber Company (later Uniroyal) patented a self-sealing fuel tank design in 1941, one of many companies involved in developing this technology during WW2. A Goodyear chemist, James Merrill, filed a patent in 1941 (published in 1947) for refining and successfully testing his method for manufacturing self-sealing tanks using a two-layer system of rubber compounds encased in a metal outer shell or the wing lining of the aircraft. By 1942, fireproof tanks had developed the first flexible fuel bladders as range extender tanks for the MkIX Spitfire. These tanks were flexible containers, made of a laminated self-sealing material like vulcanized rubber, and with as few seams as possible to minimize leak paths.
Not all fighters were fitted with the relatively new invention. Self-sealing tanks tended to be heavier with lower capacity than non-sealed tanks. Nonetheless, aircraft that were fitted with self-sealing tanks regularly took more punishment than those without, and were able to return to base. Combat experience in the Pacific war showed that the heavily protected American aircraft could sustain far more damage than the lightly armored Japanese designs without self-sealing fuel tanks (for instance, the Mitsubishi A6M Zero).
Most jet fighters and all US military rotary wing aircraft have self-sealing tanks. Military rotary wing fuel tanks have the additional feature of being crashworthy. High altitudes require the tanks to be pressurized, which makes self-sealing difficult. Newer technologies have made advances like inert foam-filled tanks to prevent detonation. This foam is open cell foam that effectively divides the gas space above the remaining fuel into thousands of small spaces, none of which contain sufficient vapor to support combustion. This foam also serves to reduce fuel slosh.
For military use, tanks are qualified to MIL-DTL-27422 (includes crashworthiness requirements) or MIL-DTL-5578 (non-crashworthy). An aircraft fuel tank sometimes consists of several interconnected fuel cells. The interconnecting hoses are typically also self-sealing.
In addition to fighter aircraft and rotorcraft, some military patrol vehicles and armored VIP limousines feature self-sealing fuel tanks. Self-sealing fuel tanks using military technology are also required in some motorsport categories.