"Air Age Debut: Introducing new features of speed, comfort and operating efficiency to air travelers is United Airlines' four-engined, five-mile-a-minute Mainliner 300 (Douglas DC-6), accommodating up to 52-56 passengers plus 6000 pounds of cargo. Airport scenes such as this emphasize the immensity of the new luxury airliners with their 117 ½ foot wing span and 100 ½ foot length." (United Air Lines Photograph)

"New Luxury Airliner: New giant of the airways, United Air Lines' five-mile-a-minute, four-engine Mainliner 300 has been making cross-country operational and training flights and visiting cities along United's coast-to-coast and Pacific Coast route prior to going into scheduled service about April 1. The Douglas-built luxury liner, commonly referred to as the DC-6, is capable of coast-to-coast flights in 8 ½ hours and will carry 52 to 56 passengers plus 5,400 pounds of cargo. United is taking delivery of 35 of these new postwar planes." (United Air Lines Photograph No. 241)

Delivered to United Airlines as NX37503 in November 1946. To Mars Aviation on 23 June 1968 and then BMR Aviation in September that year. Registration cancelled on 14 June 1976 and then to an unknown owner in Oklahoma City, OK. Further registration changes noted in January 1977 to the same owner and then reported as scrapped. (United Airlines Photograph No. 308 - 1947)