Etorofu-class escort ship

The were a group of fourteen "kaibōkan" escort vessels built for the Imperial Japanese Navy during World War II. Eight of the fourteen ships were sunk during the war. The class was also referred to by internal Japanese documents as the .
Background.
The "Shimushu"-class "kaibōkan", as with the torpedo boat, was a consequence of the 1930 London Naval Treaty, which placed limitations on the total destroyer tonnage the Imperial Japanese Navy was permitted. One way in which the treaty could be circumvented was to use a loophole in the treaty which permitted ships of between 600 and 2,000 tons, with no more than four guns over , no torpedoes, and with a maximum speed of no more than . A new class of vessel was designed to use this loophole, and was given the obsolete designation of "kaibōkan" ("Kai" = sea, ocean, "Bo" = defence, "Kan" = ship), which had previously been used to designate obsolete battleships which had been reassigned to coastal defense duties. Immediately before the start of then Pacific War, the Imperial Japanese Navy suddenly decided to give more priority to convoy escorts, possibly in light of the ongoing successes of German U-boats against British shipping in the Atlantic. As the "Shimushu" class was not suited for mass-production and took too long to build, the 1941 Rapid Naval Armaments Supplement Programme authorized thirty modified versions of the "Shimushu" class, which were designated the "Etorofu" class. However, sixteen of the projected thirty ships were subsequently re-ordered to the subsequent "Mikura", "Hiburi" or "Ukura" designs.
Production began between February 1942 and August 1943. Despite simplification, the design was still too complex for mass production and one of the ships was not completed until early 1944.
Description.
The "Etorofu" class was almost identical to the "Shimushu" class but with a simplified bow, stern and bridge structure to facilitate production. The ships measured overall, with a beam of and a draft of . They displaced at standard load and at deep load. The ships had two diesel engines, each driving one propeller shaft, which were rated at a total of for a speed of . The ships had a range of at a speed of .
As with the "Shimushu" class the main battery of the "Etorofu" class consisted of three Type 3 guns in single mounts, one superfiring pair aft and one mount forward of the superstructure. Anti-aircraft protection was by four Type 96 anti-aircraft guns in two twin-gun mounts abreast the bridge. However, for a ship supposedly designed for convoy escort, only one Model 94 depth charge launcher was installed on the quarterdeck along with a Model 3 loading frame. The number of depth charges was initially 36, but this was increased to 60 while the ships were still in production, which necessitated the deletion of the two paravanes initially in the design for minesweeping. The ships were also equipped with a Model 93 sonar and a Type 93 hydrophone.
During the Pacific War, the number of Type 96 anti-aircraft gun was increased to five triple-mounts and a varying number of single-mounts, up to 15 in total by August 1943. A Type 22 and Type 13 radar were also installed. Aa Type 97 trench mortar was also installed front of the bridge 
Operational service.
The "Etorofu" class proved to be an inadequate design by the time the final units entered service in 1944. Their speed was slower than most submarines, and with only one depth charge projector, their combat capability against the increasingly effective United States Navy submarine forces was ineffective. The "Etorofu"-class vessels were mostly deployed to the South China Sea or East China Sea as convoy escorts, but few recorded any attacks against Allied submarines. Conversely, six of the 14 ships in the class were sunk by American submarines. Of the six survivors, three were used as repatriation ships after the war, and were subsequently given as prize of war to Allied navies.
Ships in class.
Thirty ships (numbered #310 to #339) were included in the Rapid Naval Armaments Supplement Programme in 1941. These are listed below with the shipyard to which each was allocated:
While fourteen of the above ships were completed to the "Etorofu" design, eight ships - "Mikura" (#320), "Miyake" (#322), "Awaji" (#324), "Nōmi" (#326), "Kurahashi" (#327), "Chiburi" (#329), "Yashiro" (#331) and "Kusagaki" (#334) - were altered to be built to the "Mikura" design; three ships - "Hiburi" (#328), "Daitō" (#333) and "Shōnan" (#339) - were altered to be built to the "Hiburi" design; and five ships - "Ukuru" (#332), "Okinawa" (#335), "Amami" (#336), "Aguni" (#337) and "Shinnan" (#338) - were altered to be built to the "'Ukuru" design. The fourteen completed to the (original) "Etorofu" design were as follows: 