The class operated in the North Island. To facilitate their fast delivery a greater loading gauge was accepted meaning that initially they could only operate on the NIMT from Auckland to Paekakariki, and the Rotorua, Kinleith and Tokoroa branches. They were excluded from operating on many branch lines on account of their weight, and were restricted in their operations on the East Coast Main Trunk (ECMT) beyond Paeroa due to the lightly-laid line through the Karangahake and Athenree gorges. Instead the lighter DF and DB class locomotives handled traffic on this line. These restrictions were reduced as bridges were progressively strengthened, and in the case of the ECMT with the opening of the Kaimai Tunnel in 1978.