The class Q of 1901 was most likely the first class of tender locomotives originally built as 4-6-2 “Pacifics”. It arose from the need for a locomotive like the 4-6-0 class UB, but with a wide firebox to burn the low-quality lignite of New Zealand. The answer was a trailing axle that carried the large firebox. Designed by A.L. Beattie, 13 arrived in the country in 1901 and 1902.
Soon the more modern Pacific classes A and AB took over the hardest services. In 1914, the class AA was introduced as a development of the Q, but with dimensions similar to the A and AB. Later all locomotives of class G also got the same boilers as class AB. In their last years they were operated in the Otago and West Coast regions and the last one was withdrawn in 1957.