F-25 Class Minelayer:
After experimenting with large treaty-skirting minelayers during the ealry 30's Koko no Kaigun shifted back it's attention at building a sizable fleet of smaller units. For this reason a class of eight units was evisioned and planned by 1937. With an overall appearance and specifications similar to that of the Japanese built Sokutens, the new units featured the usual internal compartimentation changes when compared to their IJN siblings, simplifying internal decks layout for easier and quicker construction. A feature noticeable by the lack of waving portholes and decks usually seen on Japanese ships. The units, such planned, would have measured 75,5m overall, had a beam of 7,9 and a draft of 2,6. displacing 720T at standard load they were propelled to 20knots by diesel engines driving two propellers, for a maximum range of 2.000 nautical miles at 14knots. Armament was made up by a single 76mm gun on the forecastle -another difference from the IJN Sokutens, who sported such gun only from the second batch ships- and a twin 13mm machine gun fitted on a raised platform on the quarterdeck. The ships were able to carry 120 mines, or 2 510mm anti-submarine nets in their place, and 36 depth charges arranged in ten throwers and one projector. Named Fusetsukan 25, construction of the first unit started by fall 1937, the other seven ships, named F-26 to F-38, (four missing pennants taken by the F-29 and F-34 class units) were started by 1940 and all were commissioned between 1938 and 1941.
In September 1939, just after with the war had broke out in Europe, a second batch of eight ships, F-37 through F-44 was ordered. Identical to the original batch, those ships were started between 1940 and 1942, entering service by 1943.
Order for further eight units came in late 1941 as a war preparation, further increased to fourteen in January 1942, bringing the total count of planned units for the F-25 class to 30 vessels. This third batch of ships, starting with F-45 sported a simplified bow shape, replacing the classic double curvature stem with a straigh one to further ease and standardize construction. Other than that, a few of their ballast tanks were converted to also store fuel if needed, doubling the operational range for convoy escort. All ships were laid down between June 1942 and April 1945, ten were commissioned between mid 1943 and October 1945, four units were still under construction when Koko uprisings started in November of the same year, and were not completed.
The last unit to be commissioned was F-58, which, like most of her sisters completed after 1944, sported even more modifications dictated by wartime experience. F-58 featured much less portholes, she fitted an hydrophone and had her depth charge inventory increased, as it was the AA armament, now composed of three triple and four single 25mm machine guns. Moreover, she fitted a twin mount of the newer 40mm/60 machine gun in place of the fairly useless 76mm gun. She also recieved a Type 13 air-search and a Type 22 surface-search radar (The thiarian mattress ones proved too big for such small vssels), and sported a camouflage pattern since commissionig.
Overall, sixteen of the 26 completed units were lost during the war, most by aircrafts or submarines. half of them sinking during the last year alone, a testament to the sheer superiority gained by the US Navy by that time. Of the suviving units, F-42, F-44 and F-46 were immediately decommissioned and scrapped. F-31 and F-33 left the fleet in 1947, when Koko no Kaigun was reorganized into Koko Kaijou under the peace treaty agreements. At this point F-51, F-56 and F-58 were renamed Kouika, Ika and Kani, while F-27 and F-48 retained their old numeric denomination as they were decommissioned in 1948, kouika followed the next year after a grounding accident. Ika and Kani entered the yards the same years for a refit. They landed all their original weapons and electronics, replaced with US-built systems, a twin 40mm bofor mount and five 20mm oerlikon machine guns in three single and a twin mount.
Both remained in service until 1957 when they were decommissioned and scrapped.
Ships in class: (laid down-launched-commissioned - fate)
F-25 1937-1938-1938 - Sunk 1944
F-26 1937-1938-1939 - Sunk 1945
F-27 1938-1938-1938 - Decommissioned 1948
F-28 1938-1939-1939 - Sunk 1943
F-31 1939-1939-1940 - Decommissioned 1947
F-32 1939-1939-1940 - Sunk 1944
F-33 1939-1940-1940 - Decommissioned 1947
F-36 1940-1941-1941 - Sunk 1945
F-37 1940-1941-1942 - Sunk 1944
F-38 1941-1941-1942 - Sunk 1943
F-39 1941-1941-1942 - Sunk 1944
F-40 1941-1942-1942 - Sunk 1944
F-41 1941-1942-1942 - Sunk 1945
F-42 1941-1942-1942 - Decommissioned 1946
F-43 1942-1942-1943 - Sunk 1946
F-44 1942-1942-1943 - Decommissioned 1946
F-45 1942-1943-1943 - Sunk 1945
F-46 1942-1943-1943 - Decommissioned 1946
F-47 1942-1943-1943 - Sunk 1945
F-48 1942-1943-1944 - Decommissioned 1948
F-51 1943-1943-1944 - Renamed Kouika 1947, Grounded 1949, Decommissioned and scrapped
F-52 1943-1944-1944 - Sunk 1945
F-53 1943-1944-1944 - Sunk 1944
F-55 1944-1945-1945 - Sunk 1945
F-56 1944-1944-1945 - Renamed Ika 1947, Decommissioned 1957
F-57 1944-1945-/ - not completed
F-58 1944-1945-1945 - Renamed Kani 1947, Decommissioned 1957
F-59 1944-1945-/ - not completed
F-61 1945-/-/ - not completed
F-62 1945-/-/ - not completed