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Titanium came along in the 1950s after a process to produce it was developed. Although titanium is often used where high strength and low density (i.e., a high strength/density ratio) are required, it happens to be one of the most corrosion-resistant materials in the world. It rates just below platinum and gold in this regard as long as its oxide surface is intact. Titanium has been widely used in aircraft, first for military applications and later in commercial aircraft. It was not available in fastener form until the late 1950s. Titanium became widely used in aircraft after the development of the C-5A transport for the military. Today, based on C-5A technology, it is used extensively in alloy form (6Al-4V) for the skin fasteners of all the major commercial wide-bodied transports. Because of its light weight and because it develops an anodized surface to minimize corrosion, an aluminum alloy is used for the companion nuts. Many non-aircraft uses for titanium are currently being developed as its properties become more widely appreciated.