The German Messerschmitt Bf 109 entered service in 1937 and became the most-produced fighter in history, with nearly 34,000 built. The design philosophy of the Bf 109 was to wrap a small airframe around a powerful engine using Messerschmitt's "lightweight construction" principle, which aimed to minimize the weight and number of separate parts in the aircraft.[73] By concentrating wing, engine and landing gear weight in the firewall, the structure of the Bf 109 could be made relatively light and simple.[74] The Bf 109 was the second-smallest major fighter aircraft of World War II and the lightest in the European theater.