The gunboat Pioneer was built in Sydney in 1863 by the Australian Steam Navigation Company for the New Zealand government. The paddle-steamer was designed for use on the Waikato River. The engine room and other key parts of the vessel were well armoured. The two iron turrets or cupolas each housed a 12-pounder artillery piece.

The Pioneer and the other vessels of the river fleet were vital to the British strategy in the Waikato War (1863–64). With its shallow draught, it was able to operate as far inland as Te Rore, on the Waipa River near Te Awamutu. The Pioneer was invaluable for reconnaissance and for moving troops and supplies past the Maori defences. On the Waikato near Meremere it was hit by fire from an old ship’s gun that had been acquired by the King Movement. One round penetrated the plating and spoiled a barrel of beef.

One of the Pioneer’s turrets stood on the riverbank at Mercer for many years. After a stint as a police lock-up, it was incorporated in the township’s First World War memorial in the 1920s.