The engine suffered from an abbreviated development period due to Rolls-Royce being required to suspend Vulture development in 1940 during the Battle of Britain to concentrate its work on the Merlin, which powered the RAF's two main fighters, the Hawker Hurricane and Supermarine Spitfire, and as a consequence the reliability of the Vulture when it entered service was very poor. Apart from delivering significantly less than the designed power, the Vulture suffered from frequent failures of the connecting rod big end bearings, which was found to be caused by a breakdown in lubrication, and also from heat dissipation problems. Rolls-Royce were initially confident that they could solve the problems, but in part because of its accelerated development in 1940, the company's much smaller Merlin was already nearing the same power level as the Vulture's original specification, and so production of the Vulture was discontinued after only 538 had been built.[4]