During the Pacific War, the Imperial Japanese Army built its own transport submarine, the maru-yu, and ran it separately from the navy. The navy, for its part, built a tank. Once, a navy ship signaled to the army’s boat: Nanji wa nanimono naru ya. Sensui kanō naru ya. Who are you? Can you dive?
The two services also competed over budgets, personnel and the balance of power in the cabinet. One account argues that the army’s need was urgent rather than a matter of pride, because transport by sea was the army’s job.