Japanese Cruisers of the Seventh Squadron

The , otherwise known as the "Circle One" plan was the first of four expansion plans of the

Imperial Japanese Navy The Imperial Japanese Navy (IJN; Kyūjitai: Shinjitai: ' 'Navy of the Greater Japanese Empire', or ''Nippon Kaigun'', 'Japanese Navy') was the navy of the Empire of Japan from 1868 to 1945, Potsdam Declaration, when it was dissolved followin ...

between 1930 and the start of

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

Background

The

London Naval Treaty The London Naval Treaty, officially the Treaty for the Limitation and Reduction of Naval Armament, was an agreement between the United Kingdom, Empire of Japan, Japan, French Third Republic, France, Kingdom of Italy, Italy, and the United Stat ...

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

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

and the British

Royal Navy The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...

in terms of tonnage and numbers of capital warships. The response of the

Imperial Japanese Navy General Staff The was the highest organ within the Imperial Japanese Navy (IJN). In charge of planning and operations, it was headed by an Admiral headquartered in Tokyo. History Created in 1893, the Navy General Staff took over operational (as opposed to a ...

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 and approved by the Cabinet in November 1930, and officially ratified by the

Diet of Japan , transcription_name = ''Kokkai'' , legislature = 215th Session of the National Diet , coa_pic = Flag of Japan.svg , house_type = Bicameral , houses = , foundation=29 November 1890(), leader1_type ...

in 1931. It called for the construction of 39 new combat vessels, centering on four of the new s, and expansion of the

Imperial Japanese Navy Air Service The (IJNAS) was the air arm of the Imperial Japanese Navy (IJN). The organization was responsible for the operation of naval aircraft and the conduct of aerial warfare in the Pacific War. The Japanese military acquired its first aircraft in ...

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 A seaplane is a powered fixed-wing aircraft capable of takeoff, taking off and water landing, landing (alighting) on water.Gunston, "The Cambridge Aerospace Dictionary", 2009. Seaplanes are usually divided into two categories based on their tech ...

s, land-based

bomber A bomber is a military combat aircraft that utilizes air-to-ground weaponry to drop bombs, launch aerial torpedo, torpedoes, or deploy air-launched cruise missiles. There are two major classifications of bomber: strategic and tactical. Strateg ...

s, as well as carrier-based

attack aircraft An attack aircraft, strike aircraft, or attack bomber is a tactical military aircraft that has a primary role of carrying out airstrikes with greater precision than bombers, and is prepared to encounter strong low-level air defenses while pr ...

and

floatplane A floatplane is a type of seaplane with one or more slender floats mounted under the fuselage to provide buoyancy. By contrast, a flying boat uses its fuselage for buoyancy. Either type of seaplane may also have landing gear suitable for land, ...

attack aircraft that could be launched from

battleship A battleship is a large, heavily naval armour, armored warship with a main battery consisting of large naval gun, guns, designed to serve as a capital ship. From their advent in the late 1880s, battleships were among the largest and most form ...

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

torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...

tactics Tactic(s) or Tactical may refer to: * Tactic (method), a conceptual action implemented as one or more specific tasks ** Military tactics, the disposition and maneuver of units on a particular sea or battlefield ** Chess tactics In chess, a tac ...

.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 A submarine tender, in British English a submarine depot ship, is a type of depot ship that supplies and supports submarines. Development Submarines are small compared to most oceangoing vessels, and generally cannot carry large amounts of foo ...

''Taigei'', and two

submarine chaser A submarine chaser or subchaser is a type of small naval vessel that is specifically intended for anti-submarine warfare. They encompass designs that are now largely obsolete, but which played an important role in the wars of the first half of th ...

Table of vessels

Notes

References

* {{DEFAULTSORT:Naval Armaments Supplement Programme Imperial Japanese Navy Naval history of Japan

Background

Table of vessels

See also

Notes

References