View source for 1st Naval Armaments Supplement Programme

{{Short description|First of four Imperial Japanese Naval Expansion plans}}
{{more footnotes|date=December 2013}}
[[File:Japanese Cruisers of the Seventh Squadron.jpg|right|250px|thumb|IJN cruisers ''Mogami'', ''Mikuma'', ''Kumano'' all constructed under the "Circle One" plan]]
The {{nihongo|'''1st Naval Armaments Supplement Programme'''|マル1計画, 第一次補充計画|Maru 1 Keikaku, Dai-Ichi-Ji Hojū Keikaku}}, otherwise known as the "Circle One" plan 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 ship|capital warship]]s. 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.<ref>Evans, ''Kaigun''. page 238-239</ref>

The "Circle One" plan was submitted by the [[Ministry of the Navy of Japan|Naval Ministry]] and approved by the [[Cabinet of Japan|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 {{Sclass|Mogami|cruiser}}s, 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 [[seaplane]]s, land-based [[bomber]]s, as well as carrier-based [[attack aircraft]] and [[floatplane]] attack aircraft that could be launched from [[battleship]]s, cruisers or submarines. Attention was also given to training of pilots and air crews in [[dive bombing]] and [[torpedo]] [[Military tactics|tactics]].<ref>Evans, ''Kaigun'', page 249</ref>

In a 1932 supplement to the Circle One plan, additional funding was added for the construction of three more vessels: the [[submarine tender]] [[Japanese aircraft carrier Ryūhō|''Taigei'']], and two [[submarine chaser]]s.

==Table of vessels==
{| class="wikitable"
|-
|+Vessels{{citation needed|date=April 2020}}
|-
! width="8%" | Category
! width="5%" | Class
! width="6%" | Planned
! width="15%" |Completed
! width="15%" | Converted
|-
| [[Light cruiser]]
| {{Sclass|Mogami|cruiser|5}}
| 4
| {{ship|Japanese cruiser|Mogami|1934|2}}, {{ship|Japanese cruiser|Mikuma||2}}, {{ship|Japanese cruiser|Suzuya|1934|2}}, {{ship|Japanese cruiser|Kumano||2}}
|
|-
| rowspan="2"|[[Destroyer]]
| {{Sclass|Hatsuharu|destroyer|5}}
| 12
| {{ship|Japanese destroyer|Hatsuharu|1933|2}}, {{ship|Japanese destroyer|Nenohi|1932|2}}, {{ship|Japanese destroyer|Wakaba|1934|2}}, {{ship|Japanese destroyer|Hatsushimo|1933|2}}, {{ship|Japanese destroyer|Ariake|1934|2}}, {{ship|Japanese destroyer|Yūgure|1934|2}}
| 6 vessels were converted to ''Shiratsuyu'' class
|-
| {{Sclass|Shiratsuyu|destroyer|5}}
| 
| {{ship|Japanese destroyer|Shiratsuyu|1935|2}}, {{ship|Japanese destroyer|Shigure|1935|2}}, {{ship|Japanese destroyer|Murasame|1937|2}}, {{ship|Japanese destroyer|Yūdachi|1937|2}}, {{ship|Japanese destroyer |Harusame|1935|2}}, {{ship|Japanese destroyer|Samidare|1935|2}}
| 6 vessels were converted from ''Hatsuharu'' class
|-
| [[Torpedo boat]]
| {{Sclass|Chidori|torpedo boat|5}}
| 4
| {{ship|Japanese torpedo boat|Chidori|1933|2}}, {{ship|Japanese torpedo boat|Manazuru|1933|2}}, {{ship|Japanese torpedo boat|Tomozuru||2}}, {{ship|Japanese torpedo boat|Hatsukari||2}}
| 
|-
| Cruiser [[submarine]]
| ''[[Japanese Junsen type submarine#Junsen II (I-6 class)|I-6]]''
| 1
| {{Jsub|I-6||2}}
| 
|-
| Large sized submarine
| ''[[Kaidai class submarine#Kaidai VI|I-68]]''
| 6
| ''[[Japanese submarine I-168|I-68]]'', ''[[Japanese submarine I-169|I-69]]'', ''[[Japanese submarine I-70|I-70]]'', ''[[Japanese submarine I-171|I-71]]'', ''[[Japanese submarine I-172|I-72]]'', ''[[Japanese submarine I-73|I-73]]''
| 
|-
| Medium-sized submarine
| ''[[Kaichū type submarine#Kaichū VI (Ro-33 class)|Ro-33]]''
| 2
| ''[[Japanese submarine Ro-33|Ro-33]]'', ''[[Japanese submarine Ro-34|Ro-34]]''
| 
|-
| [[Submarine tender]]
| ''[[Japanese aircraft carrier Ryūhō|Taigei]]''
| 1
| ''Taigei''
| later converted to the [[aircraft carrier]] {{ship|Japanese aircraft carrier|Ryūhō||2}}
|-
| rowspan="2"|[[Minelayer]]
| {{ship|Japanese minelayer|Okinoshima||2}}
| 1
| ''Okinoshima''
| 
|-
| {{Sclass|Natsushima|minelayer|5}}
| 3
| {{ship|Japanese minelayer|Natsushima|1933|2}}, {{ship|Japanese minelayer|Nasami||2}}, {{ship|Japanese minelayer|Sarushima||2}}
| 
|-
| [[Minesweeper (ship)|Minesweeper]]
| ''[[No.13 class minesweeper|No.13]]''
| 6
| ''[[Japanese minesweeper No.13 (1933)|No.13]]'' to ''[[Japanese minesweeper No.18 (1936)|No.18]]''
| 
|-
| [[Subchaser]]
| ''[[No.1 class submarine chaser|No.1]]''
| 2
| ''No.1'' and ''No.2''
| 
|-
|}

==See also==
*[[2nd Naval Armaments Supplement Programme]] (Maru 2 Keikaku, 1934)
*[[3rd Naval Armaments Supplement Programme (Japan, 1937)|3rd Naval Armaments Supplement Programme]] (Maru 3 Keikaku, 1937)
*[[4th Naval Armaments Supplement Programme (Japan, 1939)|4th Naval Armaments Supplement Programme]] (Maru 4 Keikaku, 1939)
*[[Temporal Naval Armaments Supplement Programme (Japan, 1940)|Temporal Naval Armaments Supplement Programme]] (Maru Rin Keikaku, 1940)
*[[Rapidly Naval Armaments Supplement Programme (Japan, 1941)|Rapidly Naval Armaments Supplement Programme]] (Maru Kyū Keikaku, 1941)
*[[Additional Naval Armaments Supplement Programme (Japan, 1941)|Additional Naval Armaments Supplement Programme]] (Maru Tui Keikaku, 1941)
*[[5th Naval Armaments Supplement Programme (Japan, 1941)|5th Naval Armaments Supplement Programme]] (Maru 5 Keikaku, 1941)
*[[6th Naval Armaments Supplement Programme (Japan, 1942)|6th Naval Armaments Supplement Programme]] (Maru 6 Keikaku, 1942)
*[[Modified 5th Naval Armaments Supplement Programme (Japan, 1942)|Modified 5th Naval Armaments Supplement Programme]] (Kai-Maru 5 Keikaku, 1942)
*[[Wartime Naval Armaments Supplement Programme (Japan, 1944)|Wartime Naval Armaments Supplement Programme]] (Maru Sen Keikaku, 1944)

==Notes==
{{reflist}}

==References==
*{{cite book
 | last = Evans 
 | first = David 
 | year = 1979
 | title = Kaigun: Strategy, Tactics, and Technology in the Imperial Japanese Navy, 1887-1941 
 | publisher = US Naval Institute Press 
 | location = 
 | isbn = 0-87021-192-7
}}
{{IJN Naval Armnament Supplement Programs}}

{{DEFAULTSORT:Naval Armaments Supplement Programme}}
[[Category:Imperial Japanese Navy]]
[[Category:Naval history of Japan]]