aircraft. This extensive usage led to the development and construction of 'light' carriers. Escort aircraft carriers, such as , were sometimes purpose-built but most were converted from merchant ships as a stop-gap measure to provide anti-submarine air support for convoys and amphibious invasions. Following this concept, light aircraft carriers built by the US, such as , represented a larger, more "militarized" version of the escort carrier. Although with similar complement to escort carriers, they had the advantage of speed from their converted cruiser hulls. The UK 1942 Design Light Fleet Carrier was designed for building quickly by civilian shipyards and with an expected service life of about 3 years. They served the Royal Navy during the war, and the hull design was chosen for nearly all aircraft carrier equipped navies after the war, until the 1980s. Emergencies also spurred the creation or conversion of highly unconventional aircraft carriers. CAM ships were cargo-carrying merchant ships that could launch (but not retrieve) a single fighter aircraft from a catapult to defend the convoy from long range land-based German aircraft. Postwar era Before World War II, international naval treaties of 1922, 1930, and 1936 limited the size of capital ships including carriers. Since World War II, aircraft carrier designs have increased in size to accommodate a steady increase in aircraft size. The large, modern of US Navy carriers has a displacement nearly four times that of the World War II–era , yet its complement of aircraft is roughly the same—a consequence of the steadily increasing size and weight of individual military aircraft over the years. Today's aircraft carriers are so expensive that some nations which operate them risk significant economic and military impact if a carrier is lost. Some changes were made after 1945 in carriers: The angled flight deck was invented by Royal Navy Captain (later Rear Admiral) Dennis Cambell, as naval aviation jets higher speeds required carriers be modified to "fit" their needs. Additionally, the angled flight deck allows for simultaneous launch and recovery. Jet blast deflectors became necessary to protect aircraft and handlers from jet blast. The first US Navy carriers to be fitted with them were the wooden-decked s which were adapted to operate jets in the late 1940s. Later versions had to be water-cooled because of increasing engine power. Optical landing systems were developed to facilitate the very precise landing angles required by jet aircraft, which have a