inactive engine, compressor air could be crossfed from a live engine to a starter turbine. The crossfeed duct was later discovered to be a potential fire hazard. Similarly, the two hydraulic systems on board were designed to be powered by the two inner engines that would always be running. Electrical generation was designed to far exceed the consumption of existing equipment to accommodate additional systems installed over the Nimrod's service life. The standard Nimrod fleet carried out three basic operational roles during their RAF service: Anti-Submarine Warfare duties typically involved surveillance over an allocated area of the North Atlantic to detect the presence of Soviet submarines in that area and to track their movements. In the event of war, reconnaissance information gathered during these patrols would be shared with other allied aircraft to enable coordinated strikes at both submarines and surface targets. Search and rescue (SAR) missions were another important duty of the RAF's Nimrod fleet, operating under the Air Rescue Coordination Centre at RAF Kinloss, and were a common sight in both military and civil maritime incidents. Throughout the Nimrod's operational life, a minimum of one aircraft was held in a state of readiness to respond to SAR demands at all times. Avionics The Nimrod featured a crew of up to 25 personnel, although a typical crew numbered roughly 12, most of whom operated the various onboard sensor suites and specialist detection equipment. A significant proportion of the onboard sensor equipment was housed outside the pressure shell inside the Nimrod's distinctive pannier lower fuselage. Sensor systems included radar, sonar, and the magnetic anomaly detector; a 'sniffer' could detect exhaust fumes from diesel submarines as well. The Nimrod and its detection capabilities were an important component of Britain's military defence during the height of the Cold War. The Nimrod's navigational functions were computerised, and were managed from a central tactical compartment housed in the forward cabin. Various functions such as weapons control and information from sensors such as the large forward doppler radar were displayed and controlled at the tactical station. The flight systems and autopilot could be directly controlled by navigator's stations in the tactical compartment, giving the navigator nearly complete aircraft control. The navigational systems comprised digital, analogue, and electro-mechanical elements. The computers were integrated with most of the Nimrod's guidance systems such as the air data computer, astrocompass, inertial guidance and doppler radar. Navigation information could also