The Heiwa Maru was a whaling ship of Japanese origin that the Diamond Dogs utilized.
Because the International Whaling Commission "raised a stink" against whaling, Japan's whaling industry suffered, with Diamond Dogs during the nine years Big Boss and Venom Snake were in a coma purchasing it at a cheap price. Diamond Dogs, however, paid five times the bargain price to extensively upgrade the ship's communication gear and ESM systems while at the same time making the ship appear intact since its purchase. The ship was later put to use to deliver Venom Snake to Port Said for a brief layover, before transferring to the oil tanker Karachi for the remaining distance to Port Qasim during the trek to Afghanistan to rescue Kazuhira Miller from Soviet forces. Afterwards, the Heiwa Maru was primarily used for SIGINT operations across the globe, with Miller planning to use the ship as a communications relay between Venom Snake (and presumably other Diamond Dogs operatives) and Mother Base, as well as a chopper resupply vessel in the future.