World War II, there was a political conflict between supporters of
Hepburn romanization and supporters of
Nihon-shiki romanization. In 1930, a board of inquiry, under the aegis of the
Minister of Education, was established to determine the proper romanization system. The Japanese government, by cabinet order (訓令 kunrei),
 announced on September 21, 1937 that a modified form of Nihon-shiki would be officially adopted as Kunrei-shiki.
 The form at the time differs slightly from the modern form.
 Originally, the system was called the Kokutei (国定, government-authorized) system.
The Japanese government gradually introduced Kunrei-shiki, which appeared in secondary education, on railway station signboards, on nautical charts, and on the 1:1,000,000 scale
International Map of the World.
 While the central government had strong control, from 1937 to 1945, the Japanese government used Kunrei-shiki in its tourist brochures.
 In Japan, some use of Nihon-shiki and Modified Hepburn remained, however, because some individuals supported the use of those systems.
J. Marshall Unger, the author of Literacy and Script Reform in Occupation Japan: Reading between the Lines, said that the Hepburn supporters "understandably" believed that the Kunrei-shiki "compromise" was not fair because of the presence of the "un-English-looking spellings" that the Modified Hepburn supporters had opposed.
 Andrew Horvat, the author of Japanese Beyond Words: How to Walk and Talk Like a Native Speaker, argued that "by forcing non-native speakers of Japanese with no intentions of learning the language to abide by a system intended for those who have some command of Japanese, the government gave the impression of intolerant language management that would have dire consequences later on."
After the Japanese government was defeated in 1945, General
Douglas MacArthur, the
Supreme Commander for the Allied Powers issued a directive, dated September 3, 1945, that stated that
Modified Hepburn was the method to transcribe Japanese names. Some editorials printed in Japanese newspapers advocated for using only Hepburn.
 Supporters of Hepburn denounced pro-Kunrei-shiki and pro-Nihon-shiki advocates to the SCAP offices
 by accusing them of being inactive militarists
 and of collaborating with militarists. Unger said that the nature of Kunrei-shiki led to "pent-up anger" by Hepburn supporters.
 During the postwar period, several educators and scholars tried to introduce romanized letters as a teaching device and possibility later replacing
kanji. However, Kunrei-shiki had associations with Japanese militarism, and the US occupation was reluctant to promote it.
 On December 9, 1954, the Japanese government re-confirmed Kunrei-shiki as its official system
 but with slight modifications.
Eleanor Jorden, an American linguist, made textbooks with a modified version of Kunrei-shiki, which were used in the 1960s in courses given to US diplomats. The use of her books did not change the US government's hesitation to use Kunrei-shiki.
As of 1974, according to the
Geographical Survey Institute, Kunrei-shiki was used for topographical maps, and Modified Hepburn was used for geological maps and aeronautical charts.
As of 1978, the
National Diet Library used Kunrei-shiki. The
Ministry of Foreign Affairs, the
Ministry of International Trade and Industry, and many other official organizations instead used Hepburn, as did
The Japan Times, the
Japan Travel Bureau, and many other private organizations.