The airplane was landed with the landing gear retracted and veered off the runway. It collided with a ditch, resulting in substantial damage to the fuselage. An examination of the airplane by a Federal Aviation Inspector revealed that a propeller strike occurred on the centerline 1,999 feet from the approach end of the runway and continued for 843 feet. During examination, all three landing gear doors were found in the retracted position. The landing gear doors and the tip tanks displayed evidence that they scraped on the runway surface. An examination of the tires revealed that all of the tires were inflated. An examination of the cockpit revealed that the landing gear handle was in the "gear up" position. The airplane was placed on jacks, and the battery switch was turned to the "on" position. The landing gear horn was operational, and all three landing gear lights were not illuminated. The gear was manually extended, and the gear horn silenced and all three landing gear position lights illuminated green.