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. The US Navy ordered a new type of airship in 1951 for the Korean War. The new air ship was designated ZP4K (later called ZSG-4), which had a different design than WW2 K-type. The first ZP4K was delivered in June 1954. A total of 15 were built. In 1955 an update version a called the ZP5K (later called ZS2G-1) was delivered, a total of 15 were built. The ZP5K has an inverted “Y” tail.globalsecurity.org Airshiphistory.navy.mil, XV. Airship Types in the Postwar Period
