A self-sealing fuel tank is a type of fuel tank, typically used in aircraft fuel tanks or fuel bladders, that prevents them from leaking fuel and igniting after being damaged. Typical self-sealing tanks have layers of rubber and reinforcing fabric, one of vulcanized rubber and one of untreated natural rubber, which can absorb fuel, swell and expand when it comes into contact with the fuel. When a fuel tank is punctured, the fuel seeps into the layers, causing the untreated layer to swell and thus seal the puncture. A similar concept is also employed for making self-sealing run-flat tires. History World War I George J. Murdock applied for the patent "War Aeroplane Fuel Tanks" on February 7, 1917 but was temporarily blocked by an order of the Federal Trade Commission, on February 6, 1918, to keep any discussion or publication of the invention secret. The order was rescinded by the United States Patent Office on September 26, 1918 and Murdock was eventually granted United States Patent 1,386,791 "Self-Puncture Sealing Covering for Fuel-Containers" on August 9, 1921. Military aircraft built by the Glenn L. Martin Company used this self-sealing fuel tank. Howard Hughes used neoprene to self-seal his fuel tanks on his 1938 around the world flight. World War II In the newer generations of pre-war and early-war aircraft, self-sealing tanks were tanks used to minimize the damage from leaking or burning fuel. A conventional fuel tank, when hit by gunfire, could leak fuel rapidly. This would not only reduce the aircraft's range but was also a significant fire hazard. Damaged fuel tanks could also rupture, destroying the airframe or critically affecting flight characteristics. It was realized that, because of weight limitations, it was not practical to simply add armor plate to aircraft fuel tanks; a method of stopping fuel leaking from damaged tanks was necessary. Early attempts at protecting fuel tanks consisted of using metal tanks, covered inside or outside by a material that expanded after being pierced. Research revealed that the exit of the projectile, rather than the entry, was the greater problem, as it often tumbled, thus creating a larger exit hole. Among the earliest versions of these types of tanks were those manufactured in the UK at Portsmouth Airport by Fireproof Tanks Ltd (formed in 1939). These tanks were first installed in the Fairey Battle light bomber with other versions installed in Supermarine Spitfire and Hawker Hurricane