[12] Hata's second book, the 1962 work Gun fashizumu undō shi ("A History of the Military Fascist Movement"), was promoted by the historian Shuhei Domon as "a first-rate narrative interpretation based on extensive use of documentary evidence.

[12] Starting in 1968 Hata headed a team of scholars with a task from the Ministry of Education to analyze all available sources and documents on the workings of the wartime and prewar armed forces of Japan.

The fruit of their research was Nihon Rikukaigun no Seido, Soshiki, Jinji ("Institutions, Organization, and Personnel of the Japanese Army and Navy"), released in 1971, which Mark Peattie called "the authoritative reference work in the field".

[18] Soon after Hata was tasked with coordinating another collaborative research project, this one for the Finance Ministry, on the subject of the occupation of Japan by the United States after World War II.

[1] Hata co-wrote two books with Yasuho Izawa on Japanese fighter aces of World War II, both of which were described by historians as the definitive treatments of the subject.

[5][25][26] Hata's major contribution to Nanjing (Nanking) Massacre studies is his book Nankin jiken ("The Nanjing Incident"), published in 1986, which is a detailed study of the event based on Japanese, Chinese, and English sources that was later noted by historians such as Daqing Yang to be one of the few impartial works of scholarship written on the massacre during the period.

Hata argued that the Japanese Army's lack of military police and facilities to detain POWs, its ignorance of international laws, and the Chinese General Tang Shengzhi's decision to flee the city without formally surrendering, which left large number of plain-clothes soldiers within the civilian population which was followed by excessive mopping-up operations by the Japanese, among the factors which led to the slaughter.

[37] In 2003 Joshua Fogel called the book "still an authority in the field",[6] and Ritsumeikan University professor David Askew designated it "the best introductory work on the Nanjing Incident in any language".

[39] In November 1997 at a conference in Princeton University Hata was confronted by Iris Chang, author of the book The Rape of Nanking, who asked him why he doubted the testimony of Japanese POWs who had stated that hundreds of thousands of Chinese were killed in the atrocity.

[40] In the wake of this incident, similar disruptions by Chinese students who disagreed with his death toll estimate prevented Hata from speaking at a number of universities that he visited.

I would add that, on the average, living conditions in the comfort stations were practically identical to those in brothels set up for American troops during the Vietnam War.

Ianfu to senjō no sei was noted for its extensive compilation of information, being praised by historian Haruo Tohmatsu as "probably the most well documented study on the question"[48] and by Mainichi Shimbun reporter Takao Yamada as "an encyclopedia-like collection of facts on comfort women".

[49] In The International History Review, A. Hamish Ion stated that with this work Hata has succeeded in creating "a measured evaluation in the face of sensational and supposedly ill-researched studies by George Hicks and others".

[49] Hata is known as a strong opponent of the attempts by some Japanese nationalists to revise Japan's wartime history in a way that he deems ideologically biased.

Hata, whom The Wall Street Journal described as an advocate of the "we-did-wrong view" of Japanese history, has expressed grave concern about the advent of new historical revisionists seeking to apologize for Japan's wartime aggressions and absolve former Prime Minister Hideki Tojo.

[58] In 1995 Hata stepped down from a government commission on the construction of a new war museum near Yasukuni Shrine in fear that the project would be used to glorify Japan's wartime actions.

[68] In 1990 Hata argued that the recently released monologue of Emperor Hirohito, the former Emperor's recollection of wartime Japan which he recorded shortly after World War II, had likely been created to prove to the United States that he was not involved in war crimes and consequently Hata theorized that an English language translation must have also been drawn up at the same time, a theory which was mocked by right-wing scholars who felt the monologue was created as a simple historical record without ulterior motives.