Japanese history textbooks usually contain references to Unit 731, but do not go into detail about allegations, in accordance with this principle. Saburō Ienaga's "New History of Japan" included a detailed description, based on officers' testimony. The Ministry for Education attempted to remove this passage from his textbook before it was taught in public schools, on the basis that the testimony was insufficient. The Supreme Court of Japan ruled in 1997 that the testimony was indeed sufficient and that requiring it to be removed was an illegal violation of freedom of speech.