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Ever since the Montgolfier brothers performed the first hot air balloon flight over Paris in 1783, the world has been fascinated with lighter than air flight. From that first flight developed the hydrogen fed observation balloons of the Civil War, which could attain an altitude of 1,000 ft. By 1900, Count Ferdinand von Zeppelin had developed a 400 ft. long tubular-shaped airship, containing multiple gas cells for lift and capable of sustained flight. During World War I, airships were used for a number of tasks, to include reconnaissance, aerial bombardment and anti-submarine warfare. It is this mission, which will be the subject of this blog.

The United States Navy began its military blimp program in 1915, before the United States entered World War I, with the contract to the DN-1 airship, awarded to Connecticut Aircraft Company in June of that year. The designation DN-1 was the first classification of lighter than air craft by the USN, with the D for dirigible, N for non-rigid and 1 noting the first airship. Though the DN-1 was heavily damaged during a flight the following year, the Bureau of Construction and Repair was reviewing several studies for a future class of dirigibles in April 1916, with the board mandating the development of dirigibles and other lighter-than-air craft and establishing a test site at Akron, Ohio from which to test free balloons, kite balloons and non-rigid airships. Conclusions reached from the early tests at Akron indicated both balloons and airships were an easy target for enemy aircraft, as well as having restricted mobility when anchored to a ship. When the United States entered World War I in 1917, airships coordinated their operations with both flying boats and seaplanes to protect shipping along the Atlantic seaboard of the the U.S. The airships acted as a reconnaissance element to warn convoys of German U boats and mines in the path of the convoys. The airships were an effective deterrent against the U boats during the course of the war, since no shipping losses were sustained while under the escort of airships.

The U.S. Navy began to obtain non-rigid (no metal frame) airships near the end of the 1920's. The first non-rigid airship was, ironically, a metal clad construction. Built by the Aircraft Development Corporation, the ZMC-2 was the only metal-clad airship built. The ZMC-2 was delivered to the Navy in September 1929, serving on a number of humanitarian missions. While difficult to control during high winds, the craft remained in service for twelve years, logging over 2,200 flight hours. By the 1930's the Goodyear Tire and Rubber Company began to build a number of non-rigid airships, or blimps, used for civil purposes, such as barnstorming and advertising. The name blimp is derived from the cartoon character created by David Low, a British political cartoonist of the 1930's. The U.S. Navy capitalized on Goodyear's success and contracted with Goodyear to build its new fleet of airships. The first blimp was the prototype K-1, built in 1931 with Goodyear building the balloon bag and the Naval Aircraft Factory building the control car that hung below the balloon bag. The later production K airships were 253 feet long and 60 feet wide. They had a capacity of 416,000 to 425,000 cubic feet, and were powered by two 425 hp. engines giving the craft a top speed of just over 50 mph. Compared to patrol aircraft of the day, the K series blimps had a good endurance and could remain aloft for sixty hours. The K airships also burned a new type of fuel gas which resembled propane rather than the standard liquid fuel. This fuel could be contained in cells within the airship envelope, and since it had almost the same density as air, the buoyancy of the airship did not change as the fuel was burned. This stabilized the airship and was more efficient than liquid gasoline, eliminating the need to compensate for the weight of the fuel burned during flight. In 1937, the Navy assumed control of the airship program from the Army Air Corps. The improved K-2 blimp series was introduced in 1938, with the primary difference from the K-1 blimps was a slightly larger fuel capacity.

When the United States entered World War II after the attack on Pearl Harbor in December 1941, the Navy had a fleet of only ten blimps. In June 1942 Congress had authorized the production of 200 blimps. Though the blimps were a small command in terms of the overall Navy organization, they played an important role. Their missions included search and rescue, anti-submarine warfare, minesweeping, escorting convoys and reconnaissance. Though blimps were not equipped with radio detection-homing gear, they were successful in keeping radar-detecting U boats contained underwater by simply conducting long-duration patrols while using their radar. In 1944, Navy blimps were equipped with magnetic anomaly detectors (MAD) from which they were able to detect the hulls of submerged submarines. They were highly successful in this mission, effectively denying the U boats access to the Straits of Gibraltar. Toward the end of the war, Navy blimps began dropping sono-buoys, enabling them to detect nearby U boats. These, coupled with the use of homing torpedoes, increased their combat effectiveness. The tactical doctrine governing blimp operations was they were never to directly engage surfaced U boats, unless it was absolutely necessary. In July 1943, the blimp K74 detected a surfaced U boat in the Florida Straits. The blimp could see the U boat (U 134) closing in on a tanker and a freighter. The K74 attempted keep the U boat away from the ships by opening fire with its .50 caliber machine gun. The U boat, undeterred, headed for the ships. The K74 dropped two depth charges, but failed to damage the U boat. After an exchange of gunfire with the U 134's anti-aircraft guns, the K74 began a rapid descent to the sea. Nine of the ten crew assigned to the K74 survived the ordeal before being picked by a Grumman J4 amphibian the next day.

Blimp missions were highly successful during World War II, losing only one craft to enemy action, in addition to losing only one escorted ship. After the war, the Navy reduced its blimp presence, but still conducted anti-submarine patrols, air-sea rescue, as well as serving as a radar platform. The blimp program was finally terminated in August 1962. A major factor in this decision was the advent of jet technology along with long-range patrol aircraft performing many of the same missions. However, blimps served the nation during its greatest time of need, with Grossadmiral Karl Doenitz, commander of the German U boat fleet, stating after the war that few U boat commanders would approach a convoy, once they were detected by a blimp.

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