The otherwise known as the "Circle Two" Plan was the second of four expansion plans of the Imperial Japanese Navy

Imperial Japanese Navy

The Imperial Japanese Navy was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes...

 between 1930 and the start of World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

.

Background

The London Naval Treaty

London Naval Treaty

The London Naval Treaty was an agreement between the United Kingdom, the Empire of Japan, France, Italy and the United States, signed on April 22, 1930, which regulated submarine warfare and limited naval shipbuilding. Ratifications were exchanged in London on October 27, 1930, and the treaty went...

 placed severe restrictions on Japan's naval capabilities vis-a-vis the United States Navy

United States Navy

The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

 and the British Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 in terms of tonnage and numbers of capital warship

Capital ship

The capital ships of a navy are its most important warships; they generally possess the heaviest firepower and armor and are traditionally much larger than other naval vessels...

s. The respose of the Imperial Japanese Navy General Staff

Imperial Japanese Navy General Staff

The was the highest organ within the Imperial Japanese Navy. In charge of planning and operations, it was headed by an Admiral headquartered in Tokyo.-History:...

 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.

The "Circle One" plan was submitted by the Naval Ministry

Ministry of the Navy of Japan

The was a cabinet-level ministry in the Empire of Japan charged with the administrative affairs of the Imperial Japanese Navy . It existed from 1872 to 1945.-History:...

 and approved by the Cabinet

Cabinet of Japan

The of Japan is the executive branch of the government of Japan. It consists of the Prime Minister and up to fourteen other members, called Ministers of State. The Prime Minister is designated by the Diet, and the remaining ministers are appointed and dismissed by the Prime Minister...

 in November 1930, and officially ratified by the Diet of Japan

Diet of Japan

The is Japan's bicameral legislature. It is composed of a lower house, called the House of Representatives, and an upper house, called the House of Councillors. Both houses of the Diet are directly elected under a parallel voting system. In addition to passing laws, the Diet is formally...

 in 1931. It called for the construction of 39 new combat vessels, centering around four of the new Mogami-class

Mogami class cruiser

The were a class of four heavy cruisers built for the Imperial Japanese Navy in the mid-1930s. All four fought in World War II, and were sunk.-Design:...

 cruiser

Cruiser

A cruiser is a type of warship. The term has been in use for several hundreds of years, and has had different meanings throughout this period...

s, and expansion of the Imperial Japanese Navy Air Service

Imperial Japanese Navy Air Service

The Imperial Japanese Navy Air Service was the air arm of the Imperial Japanese Navy during World War II, the organization was responsible for the operation of naval aircraft and the conduct of aerial warfare in the Pacific War.It was controlled by the Navy Staff of the Imperial Japanese Navy and...

 to 14 Naval Air Groups. However, plans for a second expansion budget were delayed by the Tomozuru Incident and IJN 4th Fleet Incident, when it was revealed that the basic designs of many Japanese warships were flawed due to poor construction techniques and instability caused by attempting to mount too much weaponry on too small a displacement hull. As a result, most of the naval budget in 1932-1933 was absorbed in modifications to rectify issues with existing equipment.

In 1934, the Naval Ministry submitted its second expansion plan to the Cabinet and Diet for approval. This plan was a multiyear (four year) budget, covering the construction of 48 new warships and creation of eight new Naval Air Groups. A total of 431,680,800 Yen was allotted for warship construction and 33,000,000 Yen for naval aviation

Naval aviation

Naval aviation is the application of manned military air power by navies, including ships that embark fixed-wing aircraft or helicopters. In contrast, maritime aviation is the operation of aircraft in a maritime role under the command of non-naval forces such as the former RAF Coastal Command or a...

.

Table of vessels

Category	Class	Planned	Completed	Converted	Cancelled
Light cruiser	Tone Tone class cruiser The two were the last heavy cruisers produced for the Imperial Japanese Navy. The Tone class cruisers were originally envisaged as the 5th and 6th vessels in the Mogami class. However, by the time construction began, serious weaknesses in the Mogami-class hull design had become clear following...	2	Tone, Chikuma	Converted to heavy cruiser.
Aircraft carrier	Sōryū	2	Sōryū Japanese aircraft carrier Soryu was an aircraft carrier of the Imperial Japanese Navy. During the Second World War, she took part in the attack on Pearl Harbor, Wake Island, Port Darwin and raids in the Indian Ocean before being sunk at the Battle of Midway.-Design:...	1 vessel was converted to the Hiryū class.
	Hiryū		Hiryū Japanese aircraft carrier Hiryu was a modified Sōryū-class aircraft carrier of the Imperial Japanese Navy. She was one of the carriers that began the Pacific War with the attack on Pearl Harbor...
Destroyer	Shiratsuyu Shiratsuyu class destroyer The was a class of ten destroyers of the Imperial Japanese Navy in service before and during World War II.-Background:The initial six Shiratsuyu class destroyers were modified versions of the , and had been originally planned as the final six vessels of that class under the ”Circle-One” Naval...	4	Umikaze Japanese destroyer Umikaze was the seventh of ten s, and the first to be built for the Imperial Japanese Navy under the Circle Two Program .-History:... , Yamakaze Japanese destroyer Yamakaze was the eighth of ten s, and the second to be built for the Imperial Japanese Navy under the Circle Two Program .-History:... , Kawakaze Japanese destroyer Kawakaze was the ninth of ten s, and the third to be built for the Imperial Japanese Navy under the Circle Two Program .-History:The Shiratsuyu class destroyers were modified versions of the , and were designed to accompany the Japanese main striking force and to conduct both day and night torpedo attacks... , Suzukaze Japanese destroyer Suzukaze was the tenth and final vessel of ten destroyers, and the fourth to be built for the Imperial Japanese Navy under the Circle Two Program .-History:...
	Asashio Asashio class destroyer The was a class of ten destroyers of the Imperial Japanese Navy in service before and during World War II.-Background:The Imperial Japanese Navy was not entirely satisfied with the performance of the , particularly in terms of operational range and speed...	10	Asashio Japanese destroyer Asashio was the lead ship of the ten destroyers built for the Imperial Japanese Navy in the mid-1930s under the Circle Two Program .-History:... , Ōshio Japanese destroyer Oshio was the second of ten destroyers built for the Imperial Japanese Navy in the mid-1930s under the Circle Two Supplementary Naval Expansion Program .-History:... , Michishio Japanese destroyer Michishio was the third of ten destroyers built for the Imperial Japanese Navy in the mid-1930s under the Circle Two Supplementary Naval Expansion Program .-History:... , Arashio Japanese destroyer Arashio was the fourth of ten destroyers built for the Imperial Japanese Navy in the mid-1930s under the Circle Two Supplementary Naval Expansion Program .-History:... , Yamagumo, Natsugumo Japanese destroyer Natsugumo was the fifth of ten destroyers built for the Imperial Japanese Navy in the mid-1930s under the Circle Two Supplementary Naval Expansion Program .-History:... , Asagumo, Minegumo Japanese destroyer Minegumo was the eighth of ten destroyers built for the Imperial Japanese Navy in the mid-1930s under the Circle Two Supplementary Naval Expansion Program .-History:... , Arare Japanese destroyer Arare was the tenth and last of the destroyers built for the Imperial Japanese Navy in the mid-1930s under the Circle Two Supplementary Naval Expansion Program .-History:... , Kasumi Japanese destroyer Kasumi was the ninth of ten destroyers built for the Imperial Japanese Navy in the mid-1930s under the Circle Two Supplementary Naval Expansion Program .-History:...
Torpedo boat	Ōtori Otori class torpedo boat The were a class of eight 840 ton fast torpedo boats of the Imperial Japanese Navy.-Development:The eight ships were ordered in 1934 and were commissioned between 1936 and 1937...	16	Ōtori, Hiyodori, Hayabusa, Kasasagi, Kiji, Kari, Sagi, Hato		8 vessels were cancelled.
Cruiser submarine	I-7	2	I-7, I-8 Japanese submarine I-8 The Japanese submarine I-8 was a World War II Junsen Type J-3 Imperial Japanese Navy submarine, famous for completing a technology exchange mission to German-occupied France and back to Japan in 1943....
Large sized submarine	I-74	2	I-74 Japanese submarine I-174 Japanese submarine I-174 was a Kaidai class submarine operated by the Imperial Japanese Navy between 1938 and her sinking in 1944. She completed eight war patrols during the Pacific War. She attacked the Convoy GP55 on 16 June 1943. During her ninth war patrol she was sunk near Truk on 12 April... , I-75
Seaplane tender Type-A (10,000 tons class)	Chitose	2	Chitose Japanese aircraft carrier Chitose was a light aircraft carrier of the Imperial Japanese Navy during World War II. It should not be confused with the earlier cruiser of the same name. First laid down as a seaplane tender in 1934 at Kure Navy yard, the ship originally carried Kawanishi E7K Type 94 "Alf" and Nakajima E8N Type 95... , Chiyoda Japanese aircraft carrier Chiyoda was an Chitose class aircraft carrier of the Imperial Japanese Navy. She was originally built as a seaplane carrier, before being converted to a light carrier from March to December 1943.She was damaged in the Battle of the Philippine Sea....
Seaplane tender Type-B (9,000 tons class)	Mizuho	1	Mizuho Japanese seaplane carrier Mizuho was a seaplane carrier of the Imperial Japanese Navy during World War II. The ship was built at Kawasaki Shipbuilding at Kobe, Japan, and was completed in February 1939.-Construction:...
Submarine chaser	No.3 No.1 class submarine chaser The was a class of submarine chasers of the Imperial Japanese Navy , serving during World War II. 3 vessels were built in 1933-36 under the Maru 1 Programme and the Maru 2 Programme. They have two sub classes, this article handles them collectively....	1	No.3
Submarine chaser (Small: diesel)	No.51 No.251 class auxiliary submarine chaser The was a class of submarine chasers of the Imperial Japanese Navy , serving during World War II. 3 vessels were built in 1936 – 1939 under the Maru 2 Programme. They have two sub classes, this article handles them collectively.-Background:...	2	No.51, No.52
Submarine chaser (Small: turbine)	No.53 No.251 class auxiliary submarine chaser The was a class of submarine chasers of the Imperial Japanese Navy , serving during World War II. 3 vessels were built in 1936 – 1939 under the Maru 2 Programme. They have two sub classes, this article handles them collectively.-Background:...	1	No.53
Fleet oiler	Tsurugizaki	2	Tsurugizaki Japanese aircraft carrier Shoho Shōhō , the lead ship of her class, was a light aircraft carrier of the Imperial Japanese Navy during World War II... , Takasaki Japanese aircraft carrier Zuiho was a light aircraft carrier of the Imperial Japanese Navy. During the Second World War, she participated in many operations, including the battles of Santa Cruz, Philippine Sea and Leyte Gulf where she was finally sunk by American aircraft.-Design:...	Both Tsurugizaki and Takasaki were converted into Zuiho class aircraft carrier Zuihō class aircraft carrier The was a class of two light aircraft carriers operated by the Imperial Japanese Navy during World War II. Both ships were converted from Submarine tenders.-Development:... s prior to the war, in which both were lost during the war.
Repair ship	Akashi	1	Akashi Japanese repair ship Akashi Akashi was a Japanese repair ship, serving during the World War II. She was the only specifically designed repair ship operated by the Imperial Japanese Navy. The navy based her design on the US Navy's USS Medusa.-Construction:...