One of the most challenging tasks was reinstating the aerial refuelling system, which had been blocked off. This involved replacing the non-return valves. Twenty replacements were located on a shelf at RAF Stafford. The five aircraft were fitted with the Carousel inertial navigation system. AN/ALQ-101 electronic countermeasure pods from Blackburn Buccaneer aircraft at RAF Honington were fitted to the wings of the Vulcans on improvised pylons, using the attachment points originally intended for the Skybolt missile. The undersides of the aircraft were painted Dark Sea Grey.