The 3300/3400s were first introduced into service in 1994 as the most powerful of the electric locos on QR tracks. They were built by Clyde Engineering at Somerton (Vic) and also Kelso.

These locomotives were ordered to fill increased demand at the southern end of the Bowen Basin coal fields. The majority of the class is based at Callemondah, Gladstone except they have been working out of Jililan recently due to increased traffic.

The 3300 class locomotives are fitted out as command locos (Locotrol), while the 3400s are meant to be used as Slave/Remote units.

These locomotives are not well liked by crews due to the cramped cabs, so they mainly act as slave locomotives.