K-class blimp

The K-class non-rigid airship was a class of blimps built by the Goodyear Aircraft Company of Akron, Ohio for the United States 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. Before and during World War II, 135 K-class blimps were built, configured for patrol and anti-submarine warfare operations and were extensively used in the Navy’s anti-submarine efforts in the Atlantic and Pacific Ocean areas.

Development
The K-class blimp was a product of the austere times of the American depression. In 1937, 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. 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 the K-2—404,000 ft³ (11,440 m³)—was the largest for any USN blimp up to that time. K-2 was flown extensively as a prototype, and continued to operate testing new equipment, techniques, and performing whatever tasks were needed, including combat patrols in World War II.

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. K-3 through K-8 had only minor modifications to K-2's design, the only major change was in engines from Pratt & Whitney R-1340-16s to Wright R-975-28s. The Wright engine/propeller combination proved excessively noisy and was replaced in later K-ships with the Pratt & Whitney engines. The K-3 cost $325,000. A series of orders for more K-class blimps followed. Twenty-one additional blimps (K-9 through K-30) were ordered on 14 October 1942. On 9 January 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 ft³ (11,780 m³) and those delivered thereafter used an envelope of 425,000 ft³ (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.

Variants
After World War II, a series of modified K-class blimps were introduced to the fleet. These modified blimps were designated:


 * ZNP-K
 * The original designation of the K-class blimps. Individual blimps were identified by a sequential suffix number, e.g. ZNP-K-2, ZNPK-8 etc. etc.. In everyday use only the K and numerical suffixes were used. Batches of blimps were built with sometimes major differences, but the designations remained in the ZNP-K range, until the later versions, listed below, emerged.


 * ZPK
 * Revised designation of the ZNP-K series.


 * ZP2K
 * A larger envelope with the volume increased to 527,000 ft³ (14,923 m³), re-designated ZSG-2.


 * ZP3K
 * A larger envelope with the volume increased to 527,000 ft³ (14,923 m³), re-designated ZSG-3.


 * ZP4K
 * Delivered in 1953, retaining the 527,000 ft³ (14,923 m³) envelope volume and length of 266 ft, re-designated ZSG-4 in 1954.


 * ZP5K
 * Re-designated ZS2G-1


 * ZSG-3
 * Re-designation of the ZP3K.


 * ZSG-3
 * Re-designation of the ZP3K.


 * ZS2G-1
 * Re-designation of the ZP5K.

Operational history
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 foot 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 mi, sonobuoys, and magnetic anomaly 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 in 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.

On 1 June 1944, two K-class blimps of United States Navy (USN) Airship Patrol Squadron 14 (ZP-14) completed the first transatlantic crossing by non-rigid airships. K-123 and K-130 left South Weymouth, MA on 28 May 1944 and flew approximately 16 hours to Naval Station Argentia, Newfoundland. From Argentia, the blimps flew approximately 22 hours to Lagens Field on Terceira Island in the Azores. The final leg of the first transatlantic crossing was about a 20-hour flight from the Azores to Craw Field in Port Lyautey (Kenitra), French Morocco. The first pair of K-ships were followed by K-109 & K-134 and K-112 & K-101 which left South Weymouth on 11 and 27 June 1944, respectively. These six blimps initially conducted nighttime anti-submarine warfare operations to complement the daytime missions flown by FAW-15 aircraft (PBYs and B-24s) using magnetic anomaly detection to locate U-boats in the relatively shallow waters around the Straits of Gibraltar. Later, ZP-14 K-ships conducted minespotting and minesweeping operations in key Mediterranean ports and various escort missions including that of the convoy carrying Franklin Roosevelt and Winston Churchill to the Yalta Conference in early 1945. In late April 1945, K-89 and K-114 left Weeksville NAS in North Carolina and flew a southern transatlantic route to NAS Bermuda, the Azores, and Port Lyautey where they arrived on 1 May 1945 as replacements for Blimp Squadron ZP-14.

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 in 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 42 ft high triangular 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.

During the war, one K-ship—K-74—was lost to enemy action when it was shot down by GS U-134 (1941) on 8 July 1943. The crew was picked up eight hours later, except for one man who drowned just before being rescued.

The last "K Ship"—K-43—was retired in March 1959.

The airship control cars (gondolas) of K-28 and K-47 are on display at the New England Air Museum in Windsor Locks, CT and the National Naval Aviation Museum in Pensacola, FL, respectively.

Nuclear weapon effects tests
Several K-class blimps were used for weapon effects tests at the Nevada Test Site (NTS) during the Operation Plumbbob series of tests in 1957.

Airship designations
During the life of the K-class airship, the U.S. 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 U.S. 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 for Goodyear, the manufacturer’s letter in the Navy's designation system. The final numeral denoted the series of the vehicle within the type/model.