Earlier sections have dealt with engines which have been developed almost entirely with the object of war and destruction. The fighter engine has been pushed all the time harder and harder to obtain greater output, with increased rate of supercharge, higher critical altitude, and more power to manœuvre under all possible conditions and attitudes of the aircraft. Performance has been achieved at almost any expense, provided reliability was ensured for a given period; such items as the time between overhaul and fuel consumption have been secondary considerations. In a similar way bomber engines have been continually stepped up in power to give maximum output at rich mixture for takeoff, so as to project the greatest possible load of bombs into the air, and every attention has also been given to providing the highest weak mixture cruising power at altitude, in order to allow for the necessary power to maintain flight at a reasonable altitude during the early part of the mission, when the machine is fully loaded.