In 1943, Japan adopted the Standard Merchant Type 1K ore carrier design and work began in three private yards. The Type 1Ks were wartime designs and, unlike other Standard Merchant Types, were not based on peacetime designs. Thirty-seven ore carriers were completed, of which six were converted to emergency tankers. Twenty ore carriers were Standard Merchant Type 1Ks.

The wartime Type 1Ks included AKIKAWA, DAIGO, DAIKYO (TAIKYO), DAIZEN, DAIYOKU (TAIYOKU), GYOKUYO, KOKUSEI, HIDA, HIDAKA, HIKACHI, HINAGA (NICHIEI), HIYORI (NICHIWA), HIKANE (HIGANE), HIOKI, HYUGA, KOKKA, KOKKO, KOKUSEI, NICHIREI, NIKKYO and TATSUBATO MARUs