1st Naval Armaments Supplement Programme (Japan, 1931)

The , otherwise known as the "Circle One" plan was the first 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. Budget for the construction pap smears
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

Seaplane

A seaplane is a fixed-wing aircraft capable of taking off and landing on water. Seaplanes that can also take off and land on airfields are a subclass called amphibian aircraft...

s, land-based bomber

Bomber

A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...

s, as well as carrier-based attack aircraft and floatplane

Floatplane

A floatplane is a type of seaplane, with slender pontoons mounted under the fuselage; only the floats of a floatplane normally come into contact with water, with the fuselage remaining above water...

attack aircraft that could be launched from battleship

Battleship

A battleship is a large armored warship with a main battery consisting of heavy caliber guns. Battleships were larger, better armed and armored than cruisers and destroyers. As the largest armed ships in a fleet, battleships were used to attain command of the sea and represented the apex of a...

s, cruisers or submarines. Attention was also given to training of pilots and air crews in dive bombing and torpedo

Torpedo

The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

tactics.

In a 1932 supplement to the Circle One plan, additional funding was added for the construction of three more vessels: the submarine tender

Submarine tender

A submarine tender is a type of ship that supplies and supports submarines.Submarines are small compared to most oceangoing vessels, and generally do not have the ability to carry large amounts of food, fuel, torpedoes, and other supplies, nor to carry a full array of maintenance equipment and...

Taigei, and two submarine chaser

Submarine chaser

A submarine chaser is a small and fast naval vessel specially intended for anti-submarine warfare. Although similar vessels were designed and used by many nations, this designation was most famously used by ships built by the United States of America...

Table of vessels

Category	Class	Planned	Completed	Converted
Light cruiser Light cruiser A light cruiser is a type of small- or medium-sized warship. The term is a shortening of the phrase "light armored cruiser", describing a small ship that carried armor in the same way as an armored cruiser: a protective belt and deck...	Mogami 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:...	4	Mogami, Mikuma Japanese cruiser Mikuma was the second vessel in the four-vessel Mogami-class of heavy cruisers in the Imperial Japanese Navy. It was named after the Mikuma river in Oita prefecture, Japan.-Background:... , Suzuya, Kumano Japanese cruiser Kumano Kumano was one of four Mogami-class heavy cruiser of the Imperial Japanese Navy. She was completed at the Kawasaki Shipyard in Kobe on 31 October 1937. She displaced with a length of and a beam of , and had a top speed of...
Destroyer Destroyer In naval terminology, a destroyer is a fast and maneuverable yet long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against smaller, powerful, short-range attackers. Destroyers, originally called torpedo-boat destroyers in 1892, evolved from...	Hatsuharu Hatsuharu class destroyer The were a class of Imperial Japanese Navy destroyers in the service before and during World War II. The final two vessels in the series, completed after modifications to the design, are sometimes considered a separate "Ariake-class".-Background:...	12	Hatsuharu Japanese destroyer Hatsuharu was the lead ship of six destroyers, built for the Imperial Japanese Navy under the Circle One Program . Three were laid down in JFY 1931 and the next three in JFY 1933... , Nenohi Japanese destroyer Nenohi was the second of six destroyers, built for the Imperial Japanese Navy under the Circle One Program . Three were laid down in JFY 1931 and the next three in JFY 1933... , Wakaba Japanese destroyer Wakaba was the third of six destroyers, built for the Imperial Japanese Navy under the Circle One Program . Three were laid down in JFY 1931 and the next three in JFY 1933... , Hatsushimo Japanese destroyer Hatsushimo was the fourth of six destroyers, built for the Imperial Japanese Navy under the Circle One Program . Three were laid down in JFY 1931 and the next three in JFY 1933... , Ariake Japanese destroyer Ariake was the fifth of six destroyers, built for the Imperial Japanese Navy under the Circle One Program . Three were laid down in JFY 1931 and the next three in JFY 1933... , Yūgure Japanese destroyer Yugure was the sixth and last destroyer, built for the Imperial Japanese Navy under the Circle One Program . Three were laid down in JFY 1931 and the next three in JFY 1933...	6 vessels were converted to Shiratsuyu class
	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...		Shiratsuyu Japanese destroyer Shiratsuyu was the lead ship of ten destroyers, and first of six to be built for the Imperial Japanese Navy under the Circle One Program .-History:... , Shigure Japanese destroyer Shigure was the second of ten s, and the first to be built for the Imperial Japanese Navy under the Circle One Program . Along with the destroyer , she developed a reputation within the Imperial Japanese Navy for being "lucky" or "unsinkable", emerging as the sole surviving Japanese warship from numerous... , Murasame, Yūdachi Japanese destroyer Yudachi was the fourth of ten destroyers, built for the Imperial Japanese Navy under the "Circle One" 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 against... , Harusame Japanese destroyer Harusame was the fifth of ten s, and was built for the Imperial Japanese Navy under the "Circle One" Program . This vessel should not be confused with the earlier Russo-Japanese War-period torpedo boat destroyer with the same name.-History:... , Samidare Japanese destroyer Samidare was the sixth of ten destroyers, built for the Imperial Japanese Navy under the Circle One 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 against the...	6 vessels were converted from Hatsuharu class
Torpedo boat Torpedo boat A torpedo boat is a relatively small and fast naval vessel designed to carry torpedoes into battle. The first designs rammed enemy ships with explosive spar torpedoes, and later designs launched self-propelled Whitehead torpedoes. They were created to counter battleships and other large, slow and...	Chidori Chidori class torpedo boat The was a Imperial Japanese Navy class of torpedo boats that served during the Second World War. They proved to have too much armament for the hull and capsized shortly after completion in heavy weather. The entire class had to be rebuilt before they became satisfactory sea-boats...	4	Chidori, Manazuru, Tomozuru Japanese torpedo boat Tomozuru was one of four s of the Imperial Japanese Navy. She capsized in a storm on March 12, 1934, shortly after her completion. This incident forced the IJN to review the stability of all recently completed, under construction and planned ships. She was salvaged and put back into service after extensive... , Hatsukari
Cruiser submarine Submarine A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...	I-6	1	I-6
Large sized submarine	I-68	6	I-68 Japanese submarine I-168 I-168 was a Kaidai class submarine of the Imperial Japanese Navy during World War II. At the Battle of Midway she sank two American warships: the aircraft carrier and the destroyer . At that time she was commanded by Lieutenant Commander Yahachi Tanabe.-Early career:The submarine was completed... , I-69, I-70, I-71, I-72, I-73
Medium sized submarine	Ro-33	2	Ro-33 Japanese submarine Ro-33 Ro-33 was a Ro-33-class submarine of the Imperial Japanese Navy. Commissioned on October 7, 1935 the submarine saw action for Imperial Japanese forces during the Pacific Campaign of World War II. The submarine was sunk near Port Moresby, Papua New Guinea with all hands by the Royal Australian... , Ro-34 Japanese submarine Ro-34 Ro-34 was a Ro-33-class submarine of the Imperial Japanese Navy. Commissioned on May 31, 1937 the submarine saw action for Imperial Japanese forces during the Pacific Campaign of World War II. The submarine was sunk off the Russell Islands in the Solomons with all hands by the United States Navy...
Submarine tender Submarine tender A submarine tender is a type of ship that supplies and supports submarines.Submarines are small compared to most oceangoing vessels, and generally do not have the ability to carry large amounts of food, fuel, torpedoes, and other supplies, nor to carry a full array of maintenance equipment and...	Taigei Japanese aircraft carrier Ryuho The was a Japanese Light aircraft carrier. Sole ship of her class, she was converted from a submarine tender. During World War II she operated mainly as aircraft transport but did participate in the First Battle of the Philippine Sea.-Conversion and commission:...	1	Taigei	later converted to the aircraft carrier Aircraft carrier An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations... Ryūhō Japanese aircraft carrier Ryuho The was a Japanese Light aircraft carrier. Sole ship of her class, she was converted from a submarine tender. During World War II she operated mainly as aircraft transport but did participate in the First Battle of the Philippine Sea.-Conversion and commission:...
Minelayer Minelayer Minelaying is the act of deploying explosive mines. Historically this has been carried out by ships, submarines and aircraft. Additionally, since World War I the term minelayer refers specifically to a naval ship used for deploying naval mines...	Okinoshima Japanese minelayer Okinoshima was a large minelayer of the Imperial Japanese Navy, which was in service during the early stages of World War II. She was named after the Okinoshima Island in the Sea of Japan and the earlier...	1	Okinoshima
	Natsushima	3	Natsushima, Nasami, Sarushima Japanese minelayer Sarushima was a small minelayer of the Imperial Japanese Navy, which was in service during World War II. She was named after Sarushima Island, a small island in Tokyo Bay, offshore Yokosuka, Kanagawa...
Minesweeper Minesweeper (ship) A minesweeper is a small naval warship designed to counter the threat posed by naval mines. Minesweepers generally detect then neutralize mines in advance of other naval operations.-History:...	No.13 No.13 class minesweeper The was a class of minesweepers of the Imperial Japanese Navy , serving during 1930s and World War II. 6 vessels were built in 1931-36 under the Maru 1 Keikaku. They have two sub classes, this article handles them collectively.-Background:...	6	No.13 to No.18
Subchaser	No.1 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....	2	No.1 and No.2

Background

Table of vessels

See also