The De Havilland Mosquito and the Avro Lancaster were two of the most legendary British aircraft of all time, eclipsed only by the immortal Supermarine Spitfire in fame. They flew for the first time six weeks apart, on 25.11.1940 the Mosquito and on 9.1.1941 the Lancaster and they were both powered by the same RR Merlin engine. Commencing bomber operations over Europe in the spring of 1942, they were also produced in similar numbers (7,781 Mosquitoes and 7,377 Lancasters). Still, they served two different design philosophies: the mainstream philosophy of a slow, heavily armed bomber with a devastating payload (the mighty Lancaster), versus the alternative one of a very fast and unarmed combat aircraft made of wood, with many applications (the compact and multi-role Mosquito). A crucial question inevitably arises: which of the two was more cost/effective?