The tanker crews were well-trained for their wartime role, as their peacetime role involved refuelling fighters scrambled in response to incursions into British airspace, usually by bombers from the Soviet Union at a rate of five per week. However, long-range flights over the unfamiliar South Atlantic Ocean necessitated upgrades to the Victors' navigational equipment, notably the installation of the Delco Carousel inertial navigation system and the Omega navigation system. The tankers were themselves capable of being refuelled in flight, which meant that it was possible to set up relays of aircraft.