Pigeon Loft Designs

Navy Blimps of World War II

Tailor-made submarine hunters

Lighter-than-air ships of the United States Navy trace their development back to World War I, when both the Central Powers and the Allies used the craft in a variety of rolls. These airships were of two types, the rigid skinned or dirigible and the non-rigid or non-dirigible. The mighty Zeppelins of Germany acquired an assorted record of success and failure. Though effectively used to cause terror and mayhem over London, the great vessels often succumbed to both foul weather and allied bullets. The results of an incendiary bullet igniting a Zeppelin's hydrogen stores tended to highlight the craft's design imperfections. The Allies, for their part, restricted the use of lighter-than-air ships almost exclusively to non-combat related missions such as convoy escorts and coastal patrols. American use of non-rigid blimps for anti-submarine patrols and escort duties proved especially promising. Slow and steady, blimps made excellent observation platforms in an era dependent primarily on visual reconnaissance. Importantly, non-hazardous duty stations freed the airships to perform to their maximum capabilities - patrol at maximum range unfettered by short-ranged fighter escort - without threat of destruction.[1]

Even with the cessation of hostilities, interest in the lighter-than-air program continued. The U. S. Army and Navy as well as the Goodyear Company launched extensive research and development projects featuring dirigible and non-dirigible aircraft. Each program carefully scrutinized the advances and failures of the other research team. Years of highly competitive experimentation produced three remarkable achievements in lighter-than-air operation: improved design configuration, better component fabrication as well as a new means of buoyancy.[2] Refined aerodynamic features and reduced size increased airship speed and range. Less wind resistance equaled less fuel consumption resulting in extended flight time. Less bulk, likewise, cut drag. In addition, designers used stout metal cables to secure the gondola car directly to the blimp which further lessened air resistance. These modifications also permitted greater 'bag' capacity while reducing overall mass.[3]

In the period between the wars, bag volume increased dramatically from 80, 000 to 416, 000 cubic feet. Significantly, by 1941, improved engine plants and efficient aerodynamics increased air speed from approximately 50 miles per hour in older models to 80 miles per hour in the navy's new 'K' class blimp. Furthermore, as World War II dawned, the newer airships outperformed their predecessors in cruising capabilities, doubling the effective range of 900 miles.[4] Between the World Wars, the Goodyear Company, as part of its ongoing airship research, developed a woven fabric and synthetic rubber hybrid to encase the gas cylinders that contained the airship's helium.. This new skin considerably diminished gas defusion and therefore improved overall blimp operation.[5]

Danger was inherent in the early model blimps, mostly due to the volatility of the hydrogen gas used to lift the airships. The fiery deaths of the famed German Hendenberg as well as Italy's lesser known Roma, graphically demonstrated the hazards of such practice. In time, researchers determined helium to be a superior gas with its greatest practical quality being its non-flammable nature. Previously, the slightest spark spelled death to older airships; helium now significantly lessened that peril. Thus helium, by providing a powerful, safe substitute for hydrogen, opened new horizons in airship construction and function. Engineers designed more powerful engines and located them closer to the bag. And, significantly, helium was to be found almost exclusively within American territory. As such, the gas became a valuable, protected resource to be developed only by nations or researchers acceptable to the American government.[6]

Years of research, design modification, and extensive testing resulted in the 'K' class airship, a tailor-made submarine hunter. Whereas fixed wing aircraft had to maintain a speed of 120 miles per hour for flight, these new blimps could fly at an extremely slow speed or even hover while searching for enemy submarines. And although an airplane's flight path might directly over-fly a submarine, required operational airspeed might prevent the pilot from detecting the enemy's presence. 'K' class blimps, however, could remain on duty for twenty hours or more, covering a greater area of ocean with their thorough and methodical sweeps.[7]

Whereas the navy possessed only ten airships (four being training models unfit for sea duty) on 7 December 1941, by war's end, the navy operated 246 blimps. The airships assumed duty stations along the Pacific, Atlantic and Gulf coasts of the United States, as well as the Caribbean, the Atlantic coast of South America, the English Channel, and Mediterranean Ocean. Early in Second World War, only thirty officers and two hundred enlisted men served in the navy's lighter-than-air branch. However, by war's end seven hundred officers and seven thousand enlisted men comprised the airship program.[8]

The principal technology for acquiring submarine contacts was Magnetic Air Detection, or MAD, gear. Essentially, the air detection equipment aboard the blimps would cancel out the earth's magnetic field in a circle that was approximately thirty feet in diameter; and, as the airship moved along, the circle moved with it. Anything metal within the circle would register in the blimp. Analogous to underwater radar, the MAD gear disclosed any metallic body that the blimp overflew, whether a sunken hull or a submarine.[9] Once the MAD gear registered a possible contact, the blimp could drop depth charges on the suspected enemy submarine. Each blimp carried two to four underwater explosive devices. These depth charges contained pressure sensitive triggers set to detonate at a depth of between seventy-five and one hundred feet. In addition to depth bombs, airships also carried a high caliber machine gun to riddle any submarine foolish enough to surface.[10]

Radios were also a primary weapon of navy blimps. Though blimps were excellent for spotting an enemy submarine and taking initial combat action, surface vessels were better equipped to battle the underwater menace. Ironically, in these sophisticated, "tailor-made" submarine hunters, carrier pigeons acted as communications backup. Naval Air Station Tillamook's private newspaper stated that "the job of the station flock was to keep the lines of communication open [with] two birds . . . placed aboard every patrol airship to carry messages in case of emergency."[11]

Multiple control design required that two pilots be assigned to each 'K' class blimp. A large wheel sat between pilot and co-pilot and was hand-turned vertically to increase or lower the blimp's elevation. Responsibility for the altitude control fell to the pilot and operation of the device required him to use both hands to rapidly increase or decrease elevation. During foul weather, maintaining a steady altitude became a full-time responsibility. The co-pilot, seated on the right side of the cockpit, was primarily responsible for the directional steering apparatus.[12]

Thirteen enlisted men and three officers comprised an airship's full complement. Officers acted as pilot, co-pilot and navigator. Enlisted-duty personnel included an engineer, a radioman, a rigger, and usually a cook. Each crew member rotated duty-four hours on and four hours off. All crew members enjoyed the use of comfortable chairs, pull down beds and a full-service galley. These amenities allowed airship crew members ample opportunity to relax and rejuvenate. Such accommodations and continual crew rotation permitted blimps up to forty-eight hours of flight time, thus maximizing their submarine hunting capabilities.[13]

An instrument panel identical to the pilot and co-pilot's was located toward the back of the gondola. At this station an engineer monitored the mechanical performance of the airship. If problems occurred, they could be swiftly analyzed and necessary action implemented before small difficulties became hazardous. By example, on one patrol, the starboard engine began to shake and sputter. From his station at the mid-ship control panel, the engineer quickly ascertained what was wrong with the engine. A catwalk was lowered from the gondola to the faltering engine. The engineer crawled out onto the narrow plank and while lying on his stomach 500 feet above the blue waves effected repairs.[14]

Despite numerous advantages, the lighter-than-air program was not without severe handicaps. The greatest of all obstacles to airship operation were foul weather and high wind. A blimp tied at the ready to a mooring mast could easily be picked up by a gust of wind and stood on its nose. Officers therefore were obligated to stay aboard the airship to work the elevator controls on stormy nights. As former pilot Bruce Kelly explained, ". . . a gust would swoop down under and lift that tail up and the blimp would be [ vertical] . . [leaving the crew] facing the ground instead of the horizon."[15]

The danger of storm fronts and wind gusts increased once a blimp was airborne. On one particularly windy day, pilot Kelly could not cover the last twenty miles to Naval Air Station Tillamook because of a strong head wind. However, by turning the blimp about and cutting one engine, Kelly solely flew his airship all the way to Wilsonville, California. Undeniably, this captivity to prevailing winds hindered lighter-than-air crafts from reaching their full potential. Designers and engineers continually struggled with airship wind vulnerability. However, as long as a reliance on lighter-than-air gasses for lift remained, no remedy for the weather handicap was forthcoming.[16]

Another vulnerable area of naval blimps was the delicate texture of the hybrid material 'skin.' "The blimp's silvery body looks tight as a drum head, but symmetry depends entirely upon the pressure of helium gas inside the great envelope."[17] By way of demonstration, a single rifle bullet would easily pierce the vulcanized canvas layers, thus deflating the entire craft[18] Or if an electrician working high up in a hanger's rafters accidentally dropped a pair of pliers onto a blimp, the craft would certainly be temporarily placed out of commission. Ground crews, too, had to take extra care when walking blimps in and out of the giant hanger doorways, lest a sudden gust slam the airship into the side of the hanger. At the very least, such a collision would deflate the blimp.[19]

Lighter-than-air craft were specifically designed to hunt and combat enemy submarines. The navy wasted no time putting these special ships into service. And although far removed from the direct threat of enemy activity, the Pacific Northwest region of the United States received special priority from the Navy Department. Early in the war, the navy determined that a squadron of 'K' class airships could be used to great effect along the coasts of Oregon and Washington.