PS Pioneer was a Clyde-built paddle steamer launched in 1905, built by A. & J. Inglis at their Pointhouse shipyard for David MacBrayne.^[1] She served as a passenger and mail ship between the Kintyre peninsula and the islands Islay, Jura and Gigha for over thirty years.^[1] In 1939 she was moved to the Mallaig and Portree, Isle of Skye route, having been replaced by MV Lochiel.^[2]

In 1943, after being laid up for a year, she was requisitioned by the Admiralty and used as a Submarine Command HQ Ship at Fairlie, North Ayrshire.^[1] In 1945 the Admiralty purchased her and renamed her HMS Harbinger, but the following year her sponsons and paddles were removed and she was used as a floating laboratory at the Isle of Portland base.^[1]

Finally in 1958 she was sent to Rotterdam, Netherlands to be scrapped.^[1]