Lack of official documentation has made estimating the total number of comfort women difficult. Vast amounts of material pertaining to war crimes, and the responsibility of the nation's highest leaders, were destroyed on the orders of the Japanese government at the end of the war."When it became apparent that Japan would be forced to surrender, an organized effort was made to burn or otherwise destroy all documents and other evidence of ill-treatment of prisoners of war and civilian internees. The Japanese Minister of War issued an order on 14 August 1945 to all Army headquarters that confidential documents should be destroyed by fire immediately. On the same day, the Commandant of the Kempetai sent out instructions to the various Kempetai Headquarters detailing the methods of burning large quantities of documents efficiently.", ;"[…] , the actual number of comfort women remains unclear because the Japanese army incinerated many crucial documents right after the defeat for fear of war crimes prosecution, […]", ;;"Between the announcement of a ceasefire on August 15, 1945, and the arrival of small advance parties of American troops in Japan on August 28, Japanese military and civil authorities systematically destroyed military, naval, and government archives, much of which was from the period 1942–1945. Imperial General Headquarters in Tokyo dispatched enciphered messages to field commands throughout the Pacific and East Asia ordering units to burn incriminating evidence of war crimes, especially offenses against prisoners of war. The director of Japan's Military History Archives of the National Institute for Defense Studies estimated in 2003 that as much as 70 percent of the army's wartime records were burned or otherwise destroyed.", .</ref> Historians have arrived at various estimates by looking at surviving documentation, which indicates the ratio of soldiers in a particular area to the number of women, and replacement rates of the women. Historian Yoshiaki Yoshimi, who conducted the first academic study on the topic and brought the issue out into the open, estimated the number to be between 50,000 and 200,000.