Japan began to learn military from Europe from the Meiji Restoration. The Japanese army first took France as an example, and after the Franco-Prussian War, it changed to Prussia-Germany as its teacher. The Japanese navy has been learning from Britain. Therefore, the tradition of European officers growing beards has also been learned by Japanese officers. However, in the First World War, both sides of the European battlefield began to use chemical weapons on a large scale and had to wear gas masks. But the beard is not easy to wear. For convenience, European officers trimmed their beards into moustaches (sanitary beards, Ren Dan beards, moustaches, etc.). Japan, which followed the example of the west, learned this experience after visiting Europe after the war. So Japanese officers who used to have beards also grew moustaches.