These photos were taken by the British mission in Japan after the war ended. The place is not known, but probably at Tomiura, Chiba Prefecture. As for Type 3 Amphibous Tank, see this page.
The front float is composed of two portions like the late version of Type 2 Amphibious Tank. The design of the turret was copied from Type 1 Medium Tank. But, there is no commander cupola and a hatch like Type 2 Amphibious Tank, instead. The hull MG mount resembles that of Type 1 Medium Tank. But, it is perfect round and smaller.
There is a large double door in the rear of turret. It will be for taking out a watertight hatch of the turret ring. MG mount is installed at the left door.
The rear hull has a cylinder-shaped structure to endure a water pressure during the transport by submarine.
Reproduction or appropriation of above photographs without permission is prohibited.