The Japanese Navy had similar ideas [1] in WWII. The plan was to sail undetected to near the west coast, launch the planes, and drop some biological weapon. Basically the predecessor of today's missile-carrying submarines.
https://www.youtube.com/watch?v=gxyk84t4Q8w
They have loads of content on weird military hardware like this.
It was a box of plague fleas.
See also: Operation Cherry Blossom at Night