The 3rd Naval Armaments Supplement Programme (マル3計画, 第三次海軍軍備補充計画, Maru 3 Keikaku, Dai-San-Ji Kaigun Gunbi Hojū Keikaku) otherwise known as the "Circle Three" Plan was the third of four expansion plans of the Imperial Japanese Navy between 1930 and the start of World War II.
The response of the Imperial Japanese Navy General Staff was to initiate a construction program (Maru-1) to build 39 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, such as expansion of the Imperial Japanese Navy Air Service to 14 Naval Air Groups [1] In 1934, the Naval Ministry submitted its second expansion plan Maru-2 to the Cabinet, to make up for the shortfall in funding caused by modifications to rectify issues with existing equipment after 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.
By 1937, the term of the London Naval Treaty had expired, and the Japanese government refused overtures to participate in further disarmament negotiations.
Instead, a massive third expansion plan was officially ratified by the Diet of Japan in 1937, calling for 66 new combat vessels, centering on two of the new Yamato-class battleships and two Shōkaku-class aircraft carriers, and expansion of the Imperial Japanese Navy Air Service by 14 more Naval Air Groups.
The final three vessels (two Katori class training cruisers, plus Ikino supply ship) were funded under the 1938 Supplementary Estimates.