Prior to the outbreak of war in 1939, flight planning procedure was not generally practised in civil aviation operations except in a few outstanding cases. Such operations as the Imperial Airways transatlantic flying boat flights called for the careful compilation of a flight plan in order that an indication of the flight time could be obtained. Since the range of these boats did not provide for any very great reserve, the flight plan was obviously an essential part of the preparation for the flight. In the case of a few shorter range operations, flight planning was also carried out to a certain extent: one operator, for instance, adopted a procedure whereby departures and arrivals were made to a schedule, and the aircraft operated so as to comply with this schedule. The increase in the length of route stages and the need for more technical operation of aircraft from the economic point of view indicated the need for more general use of serious flight planning, and it is now well established that flight planning is essential to the safe and efficient operation of flights of all kinds.