Blimps and Dirigibles differ in their size and construction. The blimp consists of a gas‐filled inflatable bag, pressurized to retain its aerodynamic shape, and attached to a rigid keel that supports a crew compartment and engines. The dirigible, roughly three times larger but otherwise similar in appearance, has vanished from the skies. It had a rigid aluminum frame that embraced several gas cells, maintained the ship's shape, and anchored the control cabin and engine pods, suspended outside a fabric‐covered hull.

In 1908, the U.S. Army purchased its first steerable, gasoline‐powered airship; with a heavy keel attached to the cigar‐shaped gas bag, it foreshadowed the blimp. The program lapsed in 1912, and during World War I the service employed only tethered observation balloons. The postwar army's Italian‐built blimp Roma, inflated with inflammable hydrogen, exploded in 1922. The use of helium, a noninflammable lifting gas, prevented further explosions, but the army gradually lost interest in lighter‐than‐air craft, except for tethered observation or barrage balloons, and in 1938 handed over its last blimps to the navy.

The U.S. Navy acquired its first blimps in 1917 and used them for coastal patrol during World War I. Navy interest soon shifted to the dirigible, a craft that seemed ideal for over‐ocean reconnaissance because its lifting gas enhanced aerodynamic efficiency: it could cruise up to 6,000 miles before refueling. Some dirigibles were over 750 feet long and could launch and recover small scouting airplanes, further extending their range.

The navy's dirigible program, encouraged by Rear Adm. William A. Moffett, began with a disaster. The first craft—modeled on a German design, built in Britain, and filled with hydrogen—exploded in 1921 while being test‐flown by an Anglo‐American crew. Misfortune plagued the navy's program. Shenandoah (1923–25) broke up in a thunderstorm, as did Akron (1931–33). Macon (1933–35) crashed because of structural failure. In effect, the destruction of Macon in 1935 signaled the end of the dirigible program. The navy's General Board rejected a five‐year procurement plan (1937–41) that would have replaced both Akron and Macon and built a new metal‐clad airship.

Navy blimps, some of them 253 feet in length, escorted coastal convoys during World War II, operating over the Pacific, the Gulf of Mexico, the Caribbean, the Atlantic, and the Mediterranean. The airships used radar to locate surfaced submarines and magnetic detectors to spot submerged U‐boats; their number peaked in March 1944 at 119. The blimp continued maritime reconnaissance after the war, and in 1956 radar‐equipped versions began guarding against possible aerial attack. Plans called for one early warning squadron on the Atlantic Coast and another on the Pacific, but only the unit based at Lakehurst, New Jersey, was actually commissioned. In October 1961, all blimp operations, including air defense missions, came to an end, though experimental flights continued until 31 August 1962. Proposals to revive the airship as a tool of war have surfaced since 1962, but none has evoked more than passing interest.

Bibliography

Douglas H. Robinson and and Charles L. Keller , “Up Ship”: A History of the U.S. Navy's Rigid Airships, 1919–1935, 1982.
William F. Althoff , Sky Ships: A History of Airships in the United States Navy, 1990.

Bernard C. Nalty