Prewar, the Japanese began construction of merchant tankers built to standard designs by private yards. The War Standard 1TM was almost identical in design. The chief difference between peacetime and wartime standards was the quality of the construction. For example, peacetime ships had a moulded stern whereas wartime ships used straight (unbent) pieces of plate wherever possible to speed up construction and because there were limited numbers of skilled shipbuilders available. The first series of wartime standards were, by and large, not too bad, but the second series made huge numbers of economies; for example, dispensing with the funnel casing altogether.

Seven tankers of the 1TM design were begun in peace time including SEISHIN, NICHINAN, NICHIRIN, NANEI, ICHIYO, PALEMBANG and OTOSISAN MARUs.

Thirty-four tankers of the 1TM design were completed during the war including ASANAGI, ASASHIO, BANEI, BOKUEI, EIHO, MENEI, MUTSUEI, NICHINAU, RYUEI, SHIMPO, TARAKAN, TENNAN and YUHO MARUs and EIYO MARU No. 2 and 20 others.