The United Aircraft and Transport Corporation was formed in 1929, when William E. Boeing teamed up with Frederick Rentschler of Pratt & Whitney.

With headquarters at Hartford, Connecticut, the holding company controlled the stock of the Boeing Airplane Company of Seattle, the Chance Vought Corporation, the Hamilton Aero Manufacturing Company (a propeller manufacturer) and the Pratt & Whitney Aircraft Company, the well known engine manufacturer. Sikorsky Aviation Corporation, the Stearman Aircraft Company of Wichita, Kansas, and the Standard Steel Propeller Company were added to United's empire shortly thereafter, followed by several more airlines brought into the fold. The airline interests were soon grouped under a new management company known as United Air Lines, Inc. However, the individual airlines (as well as the individual companies held by United) continued to operate under their own names.

In 1934, the U.S. government concluded that such large holding companies as United Aircraft and Transport were anti-competitive, and new antitrust laws were passed forbidding airframe or engine manufacturers from having interests in airlines. United Aircraft and Transport was broken up. Its manufacturing interests east of the Mississippi River (Pratt & Whitney, Sikorsky, Vought and Hamilton Standard Propeller Company) were organized into a new United Aircraft Corporation (now United Technologies Corporation). Boeing acquired the western manufacturing interests. United Airlines became a separate company.