1st Naval Armaments Supplement Programme

First of four Imperial Japanese Naval Expansion plans December 2013 right|250px|thumb|IJN cruisers Mogami, Mikuma, Kumano all constructed under the "Circle One" plan The 1st Naval Armaments Supplement Programme 第一次補充計画 Dai-Ichi-Ji Hojū Keikaku, otherwise known as the "Circle One Plan" マル1計画 Maru 1 Keikaku was the first of four expansion plans of the Imperial Japanese Navy between 1930 and the start of World War II. Background The London Naval Treaty placed severe restrictions on Japan's naval capabilities vis-a-vis the United States Navy and the British Royal Navy in terms of tonnage and numbers of capital warships. The response of the Imperial Japanese Navy General Staff was to initiate a construction program to build new warships to the allotted tonnage limits in each of the restricted categories, and to invest in types of warships and weaponry not specifically covered by the provisions of the treaty.Evans, Kaigun. page 238-239 The "Circle One" plan was submitted by the Naval Ministry and approved by the Cabinet in November 1930, and officially ratified by the Diet of Japan in 1931. It called for the construction of 39 new combat vessels, centering on four of the new Mogami cruisers, and expansion of the Imperial Japanese Navy Air Service to 14 Naval Air Groups. Budget for the construction of the warships was on a six-year basis, and the budget for forming the air groups was on a three-year basis. Total funding allotted was 247,080,000 Yen for ship construction and 44,956,000 Yen for naval aviation expansion. In terms of naval aviation development, the "Circle One" plan also concentrated on the development of new aircraft technologies, especially large seaplanes, land-based bombers, as well as carrier-based attack aircraft and floatplane attack aircraft that could be launched from battleships, cruisers or submarines. Attention was also given to training of pilots and air crews in dive bombing and torpedo tactics.Evans, Kaigun, page 249 In a 1932 supplement to the Circle One plan, additional funding was added for the construction of three more vessels: the submarine tender Taigei, and two submarine chasers. Table of vessels +VesselsApril 2020 Category Class PlannedCompleted Converted Light cruiser Mogami cruiser 5 4 Japanese cruiser Mogami 1934 2, Japanese cruiser Mikuma 2, Japanese cruiser Suzuya 1934 2, Japanese cruiser Kumano 2Destroyer Hatsuharu destroyer 5 12 Japanese destroyer Hatsuharu 1933 2, Japanese destroyer Nenohi 1932 2, Japanese destroyer Wakaba 1934 2, Japanese destroyer Hatsushimo 1933 2, Japanese destroyer Ariake 1934 2, Japanese destroyer Yūgure 1934 2 6 vessels were converted to Shiratsuyu class Shiratsuyu destroyer 5 Japanese destroyer Shiratsuyu 1935 2, Japanese destroyer Shigure 1935 2, Japanese destroyer Murasame 1937 2, Japanese destroyer Yūdachi 1937 2, Japanese destroyer Harusame 1935 2, Japanese destroyer Samidare 1935 2 6 vessels were converted from Hatsuharu class Torpedo boat Chidori torpedo boat 5 4 Japanese torpedo boat Chidori 1933 2, Japanese torpedo boat Manazuru 1933 2, Japanese torpedo boat Tomozuru 2, Japanese torpedo boat Hatsukari 2 Cruiser submarine I-6 1 I-6 2 Large sized submarine I-68 6 I-68, I-69, I-70, I-71, I-72, I-73 Medium-sized submarine Ro-33 2 Ro-33, Ro-34 Submarine tender Taigei 1 Taigei later converted to the aircraft carrier Japanese aircraft carrier Ryūhō 2Minelayer Japanese minelayer Okinoshima 2 1 Okinoshima Natsushima minelayer 5 3 Japanese minelayer Natsushima 1933 2, Japanese minelayer Nasami 2, Japanese minelayer Sarushima 2 Minesweeper No.13 6 No.13 to No.18 Subchaser No.1 2 No.1 and No.2 See also 2nd Naval Armaments Supplement Programme (Maru 2 Keikaku, 1934) 3rd Naval Armaments Supplement Programme (Maru 3 Keikaku, 1937) 4th Naval Armaments Supplement Programme (Maru 4 Keikaku, 1939) Temporal Naval Armaments Supplement Programme (Maru Rin Keikaku, 1940) Rapidly Naval Armaments Supplement Programme (Maru Kyū Keikaku, 1941) Additional Naval Armaments Supplement Programme (Maru Tui Keikaku, 1941) 5th Naval Armaments Supplement Programme (Maru 5 Keikaku, 1941) 6th Naval Armaments Supplement Programme (Maru 6 Keikaku, 1942) Modified 5th Naval Armaments Supplement Programme (Kai-Maru 5 Keikaku, 1942) Wartime Naval Armaments Supplement Programme (Maru Sen Keikaku, 1944) Notes References Evans David 1979 Kaigun: Strategy, Tactics, and Technology in the Imperial Japanese Navy, 1887-1941 US Naval Institute Press 0-87021-192-7 Category:Imperial Japanese Navy Category:Naval history of Japan