 In operations "Otago" needed the support of an RAN tanker due to the relatively short range of the Type 12 frigates which was just sufficient for a one way trip from Auckland to Mururora or to operate for 36 hours at in all-out anti-submarine operations in the Greenland-Iceland-UK gap.The "Rothesay"s were designed for such sweeps and as aircraft carrier escorts with fleet tankers in the group  sprinting and searching.A 50% fuel reserve was held at all times due to need to allow for emergency, weather and barnacle build-up on hull.