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 warships. 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 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. In addition, 48 new warships and creation of eight new Naval Air Groups were funded. 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. This plan was a multiyear (six year) budget, and allocated a total of 806,549,000
Yen was allotted for warship construction and 75,267,000 Yen for
naval aviation. The final three vessels (two
Katori class training cruisers, plus
Ikino supply ship) were funded under the 1938 Supplementary Estimates. ==Table of vessels==