Who first built and operated an amphibious assault ship?

Was Japan the first to envision and operate an amphibious assault ship?

Japan was first to build and operate the concept, but several navies were exploring it during the 1920s.

Several navies developed amphibious assault ship concepts during the 1920s after the experience of World War I. Japanese forces were the first to build and operate the idea. That priority in construction does not establish that Japan alone originated the concept. The example illustrates parallel development, with several countries working toward related solutions before one put a ship into service.