For the operations at the river and sea, the IJA produced many kinds of vessel, i.e. landing crafts, motorboats, gun boats, landing ships etc. In the Pacific War, they built even aircraft carriers and submarines.
Besides the engineer units for the river-crossing, the IJA had their own shipping force to transport troops at sea. It was a large force which employed 300,000 soldiers at maximum and managed 30% of Japanese transport ships.
For the IJA, the Pacific War was not only the battle on the ground, but also the battle at sea. Many IJA soldiers fought on the board against enemy submarines, PT boats and airplanes. At last, they rode on an explosive boat and dashed into the enemy ship.