The United Aircraft and Transport Corporation was formed in 1929, when William Boeing of Boeing Airplane & Transport Corporation teamed up with Frederick Rentschler of Pratt & Whitney to form a large, vertically integrated, amalgamated firm, uniting business interests in all aspects of aviation—a combination of airframe and aircraft engine manufacturing and airline business, to serve all aviation markets, both civil aviation (cargo, passenger, private, air mail) and military aviation.

The holding company controlled the stock of several United Equipment Companies, including the Boeing Airplane Company of Seattle, the Northrop Aircraft Corporation, the Chance Vought Corporation, the Hamilton Aero Manufacturing Company (a propeller manufacturer), and the Pratt & Whitney Aircraft Company, the Sikorsky Aviation Corporation, the Stearman Aircraft Company of Wichita, Kansas. United Transport Companies included Boeing Air Transport, Pacific Air Transport, and Stout Air Services. Other United Operations included the Boeing School of Aeronautics, United Aircraft Exports, United Airports Company of California, which built an airport at Burbank, and the United Airports of Connecticut, which built factories in East Hartford for Pratt & Whitney and Chance Vought. The first annual report lists William Boeing as chairman, Frederick Rentschler as president, and Chance M. Vought, Philip G. Johnson, and George Wheat as vice presidents.^[1]

The Standard Steel Propeller Company were added to United's portfolio shortly thereafter, followed by several airlines also 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.

After the Air Mail scandal of 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 aircraft engine manufacturers from having interests in airlines. This law forced United Aircraft and Transport to split into three separate companies. Its manufacturing interests east of the Mississippi River (Pratt & Whitney, Sikorsky, Vought, and Hamilton Standard Propeller Company) were merged as United Aircraft Corporation (later United Technologies Corporation), headquartered in Hartford, Connecticut, with Rentschler as president. The western manufacturing interests (including Northrop Aviation Corporation, formerly Avion Corporation), became Boeing Airplane Company, headquartered in Seattle. The airline interests were merged into a single airline, United Air Lines, Inc.,^[2] headquartered in Chicago.