Why the Japanese Army built an amphibious assault ship

Did Japan invent the amphibious assault ship?

Japan built the concept first, but several countries developed the idea; the Japanese Army's desire for independence from the Navy helped drive construction.

The Japanese claim to priority concerns building the amphibious assault ship concept, which several countries had already been developing. Ideas circulated in the 1920s after experience in World War I. The additional explanation here is institutional: the Japanese Army wanted greater independence from the Navy. That service relationship helped turn a broadly discussed concept into an actual ship.