Never heard of a bahto sword. There is a term BATTO, as in batto-jutsu, connected with Japanese swordsmanship. It is my understanding, limited as it is, that this refers to Japanese military swordsmanship of the 20th century, which is derived from more ancient preserved forms of kenjutsu. I do not believe it refers to the sword itself. I would suggest you ask about this on
www.e-budo.com's forum.