Mikura-class escort ship

The Mikura-class escort ships (御蔵型海防艦) were a class of eight kaibōkan escort vessels built for the Imperial Japanese Navy during World War II. Five of the eight ships were sunk during the war. The class was also referred to by internal Japanese documents as the "B-class" coastal defense vessel (乙型海防艦).

Background
The Mikura-class kaibōkan, as with the Chidori-class torpedo boat 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 76mm, no torpedoes, and with a maximum speed of no more than 20 knots. 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. The first of these vessels were the Shimushu-class escort ship and Etorofu-class escort ship; however, after the start of the Pacific War, it became apparent that a design more capable of anti-submarine warfare was needed. The 1941 Rapid Naval Armaments Supplement Programme authorized eight of these new vessels, which were designated the Mikura-class.

Production began in late 1942 concurrently with later Etorofu-class vessels.

Description
Although the Mikura-class was based on the two previous classes of escort vessels and used a simplified version of the Etorofu-class hull, it presented a much different appearance, with a stepped bridge, smaller single smokestack located further aft, shape of the aft deckhouse, and the type of main gun.

The ships measured 77.7 m overall, with a beam of 9.1 m and a draft of 3.05 m. They displaced 940 LT at standard load and 955 LT at deep load. The ships had two diesel engines, each driving one propeller shaft, which were rated at a total of 4400 bhp for a speed of 19.5 kn. The ships had a range of 5000 nmi at a speed of 16 kn.

The main battery of the Mikura-class consisted of three Type 10 120 mm AA guns — one in a enclosed turret forward and two in an open twin mount aft. These were dual-purpose guns capable of attacking both surface and aircraft targets. Anti-aircraft protection was by four Type 96 25 mm anti-aircraft guns in two twin-gun mounts abreast the bridge. The Mikura class was initially armed with 120 Type 95 depth charges with two Type 94 depth charge launchers and had a Model 93 sonar and a Type 93 hydrophone.

Later in the war, a third Type 94 depth charge launcher was added on the stern and the paravanes were removed. During the Pacific War, the number of Type 96 anti-aircraft guns was increased with the addition of a triple-mount in front of the bridge and an additional four single-mounts. A Type 22 and a Type 13 radar were also added. A Type 97 81 mm trench mortar was also installed front of the bridge

Operational service
All eight vessels in the class saw extensive combat service in the South China Sea and the East China Sea, where they were used for convoy escort. Two American submarines may have been destroyed by Mikura-class vessels, with Chiburi given credit for the sinking of USS Growler (SS-215) on 8 November 1944 and Mikura given credit for assisting in the destruction of USS Trigger (SS-237) on March 28, 1945. Of the eight vessels in the class, five were lost in combat (four to USN submarines). One ship survived the war to be used for repatriation duties and one was given as a reparations to the Republic of China Navy, under whose flag it continued to serve until scrapped in 1963.