The Union Steam Ship Co., which was established in 1876, soon had some fine vessels in its early fleet. One of these was the Rotomohana, launched in June 1879 from Denny Bros. yard at Dumbarton. With her well raked funnel and masts, shapely clipper bow with figurehead, decorative scroll work, and jib boom, she had the appearance of a steam yacht and was indeed a beautiful ship. She was the first merchant steamer to be built of mild steel and fitted with bilge keels. Her compound engines developed 2,500 h.p. from six boilers working at a pressure of 70 lb per square inch. Later she was given four new boilers and the working pressure raised to 90 lb. Her measurements were length, 298 ft, breadth, 35 ft, and depth to main deck, 23 ½ ft. Her voyage to New Zealand was the fastest to date, and she reached up to 17 knots when assisted by her sails and a following wind. On trials her maximum speed was 15.386 knots.

For nearly 20 years the Rotomohana was employed in the intercolonial trade and then, until the arrival of the Maori, was on the Wellington-Lyttelton run. In February 1904 she did this trip in 10 hours 35 minutes. From May 1908 to 1921 she ran from Melbourne to Launceston and was broken up in 1925.