K-Class Blimp

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The ZNP-K (K-class) non-rigid airship was a class of blimps built by the Goodyear Aircraft Company of Akron, Ohio for the US Navy. These blimps were powered by two radial air-cooled engines mounted on outriggers on the side of the control car that hung under the envelope. During World War II over one hundred K-Class blimps were built, configured for patrol and anti-submarine warfare operations and were the backbone in the Navy’s aniti-submarine efforts in the Atlantic and Pacific Ocean areas.

[edit] Origins

The K-Class blimp was a product of the austere times of the American depression. The first article produced in 1931 was designated K-1. It was a combined development of the Goodyear Aircraft Company and the Naval Aircraft Factory. The envelope was built by Goodyear while the Naval Aircraft Factory built the control car. The capacity of the envelope was 320,000 cubic feet (9,061 m³). The experimental K-1 introduced a number of new features to blimp design. The engines used a gaseous fuel (similar to propane), instead of normal liquid gasoline, that was stored in cells (ballonets) within the envelope. Since the gas had nearly the same density as air, the problems of ballasting for weight loss as the fuel was used were relieved. The K-1 also was the first Navy blimp that used internal suspension for hanging the control car on the envelope. Testing of the K-1 began on October 7, 1931. At the time, the K-1 was the largest non-rigid airship used by the Navy. The last flight of the K-1 was in September 1940. It was disassembled in 1941 and was stricken from the records.

In 1937, the K-2 was ordered from Goodyear as part of a contract that also bought the L-1. The L-Class was Goodyear’s standard advertising and passenger blimp. The K-2 was the production prototype for future K-class airship purchases. K-2 flew for the first time at Akron, Ohio on December 6, 1938 and was delivered to the Navy at NAS Lakehurst, New Jersey on December 16. The envelope capacity of 404,000 cubic feet (11,440 m³) for K-2 was substantially greater than that of K-1.

[edit] Production

On October 24, 1940, the Navy awarded a contract to Goodyear for six airships (K-3 through K-8) that were assigned the designation Goodyear ZNP-K. These blimps were designed for patrol and escort duties and were delivered to the Navy in late 1941 and early 1942. A series of orders for more K-class blimps followed. Twenty one additional blimps (K-9 through K-30) were ordered on October 14,1942. On January 9, 1943. 21 more blimps (K-31 through K-50) were ordered. The envelope size of K-9 through K-13 was increased to 416,000 cubic feet (11,780 m³) and those delivered thereafter used an envelope of 425,000 cubic feet (12,035 m³). The final contract for the K-class blimp were awarded in mid 1943 for 89 airships. Four blimps from this order were later canceled. The remaining deliveries were assigned numbers K-51 through K-136. But, the number K-136 was not assigned to a specific airship as the control car assigned for K-136 was used to replace the car for K-113. The original car for K-113 was destroyed in a fire.

After World War II, a series of modified K-Class blimps were introduced to the fleet. These modified blimps were designated ZP2K, ZP3K, ZP4K, and ZP5K. The ZP2K and ZP3K used a larger envelope, one with the volume increased to 527,000 cu ft (14,923 m³). Under the 1954 airship designation changes, these blimps became the ZSG-2 and ZSG-3, the ‘S’ signifying that the mission assigned to the airships was anti-submarine warfare. The ZP4K was delivered in 1953. It retained an envelope volume of 527,000 cu ft (14,923 m³) but it had an overall length of 266 ft (81.08 m). In 1954 it was re-designated ZSG-4. The ZP5K was delivered the following year, 1954. It was a much modified version of the basic K-ship, with an envelope volume increase further to 650,000 cu ft (18,406 m³) with a length of 258 feet (78.64 m). It was powered by two Wright R-1300 radial air-cooled engines of 800 hp (597 kW) each. In the re-designation in 1954, the significance of the extensive modifications was recognized in the assignment of a new model designator, ZS2G-1.

[edit] Operations

The K-ships were used for anti-submarine warfare (ASW) duties in the Atlantic and Pacific Oceans as well as the Mediterranean Sea. All equipment was carried in a forty feet long control car. The installed communications and instrumentation equipment allowed night flying. The blimps were equipped with the ASG-type radar, that had a detection range of 90 miles (167 km), sonobuoys, and magnetic anomaly detection (or magnetic airborne detection (MAD)) equipment. The K-ships carried four Mk-47 depth bombs, two in a bomb bay and two externally, and were equipped with a 50-cal (12.7 mm) Browning machine gun in the forward part of the control car. An aircrew of 10 normally operated the K-ships, consisting of a command pilot, two co-pilots, a navigator/pilot, airship rigger, an ordnanceman, two mechanics, and two radiomen.

The ability of the K-ships to hover and operate at low altitudes and slow speeds resulted in detection of numerous enemy submarines as well as assisting is search and rescue missions. The K-ships had an endurance capability of over 24 hours which was an important factor in the employment of ASW tactics.

The mooring system for the K-ship was a triangular 42 feet (12.8 m) high mooring mast that was capable of being towed by a tractor. For advance bases where moving the mooring mast was not needed, a stick mast was used. A large ground crew was needed to land the blimps and moor them to the mast.

[edit] Airship Designations

During the life of the K-Class airship the US Navy used three different designation systems. From 1922 through World War II the Navy used a four character designator. The K-Class blimps were designated ZNP-K where the “Z” signified lighter-than-air; “N” denoted non-rigid; “P” denoted a patrol mission; and “K” denoted the type or class of airship.

In April 1947, the General Board of the US Navy modified the designation system for airships. The second character of the designator was dropped as the Board dropped the code for rigid airships so that the “N” for non-rigid was no longer needed. The designation for the K-Class blimps then became ZPK.

In April 1954, the designation system for lighter-than-air airships was further modified so that it conformed to the designation system for heavier-than-air aircraft. By this time the ZPK blimps had been retired from service and only the later version K-Class blimps were in service. Under the 1954 system the ZP2K blimp became the ZSG-2, the ZP3K became the ZSG-3, the ZP4K became the ZSG-4, and the ZP5K became the ZS2G-1. In new designation system, the “Z” signified lighter-than-air; the “S” was the type denoting an anti-submarine warfare mission; the numeral (i.e., “2”) was the model; and the “G” was the manufacturer’s letter. The final numeral denoted the series of the vehicle within the type/model.

[edit] Specifications (K-14)

[edit] General characteristics

• Crew: nine or ten
• Volume: 12,043 cu m (425,000 cu ft)
• Length: 76.2 m (250 ft)
• Width: m ( ft)
• Height: m ( ft)
• Empty: kg ( lb)
• Loaded: kg ( lb)
• Powerplant: Two Pratt & Whitney R-1340 AN-2 Wasps, 448 kW (600 hp)

[edit] Performance

• Maximum speed: 120 km/h (65 knots)
• Range: 3,700 km (2,000 nautical miles)

[edit] Armament

• Four 350 lb (159 kg) Mk-47 depth bombs
• One 50-cal (12.7 mm) Browning machine gun