On August 26, 2018, about 1150 mountain daylight time, a Beech 35 airplane, N666WW, lost engine power shortly after takeoff from the Bowman Regional Airport (KBWW), Bowman, North Dakota. The commercial pilot sustained serious injury and the passenger sustained minor injuries. The airplane sustained substantial damage. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no Federal Aviation Administration (FAA) flight plan had been filed for the flight.According to the pilot, the cross-country flight was originating at the time of the accident and was en route to Dickinson-Theodore Roosevelt Regional Airport (KDIK), Dickinson, North Dakota. Shortly after takeoff, about 400 ft agl, the engine started "sputtering" and lost power. The pilot turned on the fuel pump and attempted to restore engine power without success. The pilot performed a forced landing to a field. During the landing, both main landing gear were pushed up through the wings and both wing spars were substantially damaged. According to the FAA inspector who responded to the accident site, both main fuel tanks were full of fuel. Further examination revealed that there was no fuel in the fuel lines, fuel, pump, or engine, forward of the airplane firewall and fuel selector. The fuel selector valve was found in the "OFF" position. An examination of the airplane, fuel system, and engine, conducted by the National Transportation Safety Board and FAA, revealed no mechanical anomalies that would have precluded normal operations.