Built in Kiel, Germany in 1924. They traded to Central America as Rio Panuco and Rio Bravo but during the Great Depression the company owning them (H. Schuldt of Flensburg) went bankrupt.
Sold in 1931 to the Norddeutscher Lloyd Line of Bremen, who renamed the ship Neptun and by 1934 ran them on the service between New Guinea and Hong Kong. This was in competition with Burns Philp, who asked the Australian Government to prevent them from operating out of New Guinea. The Government declined and instead offered to pay the interest on any money Burns Philp borrowed to buy them. This was agreed and they were purchased in 1935. Neptun was renamed Neptuna.
Neptuna operated on the Australia, New Guinea, Philippines, Hong Kong, Saigon Service. At the time, Saigon was then the main supply source for rice to New Guinea.
On June 20, 1931, Neptuna came to the aid of MV MacDhui that suffered a fire, towing her to Salamaua.
On February 19, 1942 while discharging munitions at Darwin Harbor when Japanese Navy aircraft attacked. Bombs exploded in the saloon and engine room setting her on fire. Forty five were already dead, and many seriously injured as the crew prepared to abandon her, but 200 tons of depth charges exploded before they had all reached safety, showering the harbor with debris and sending flames and smoke 100 meters into the air.