The company's many divisions enabled BAT the advantage of exclusively flying Boeing-designed aircraft equipped with Pratt & Whitney-produced engines. One of the best examples of their synergistic relationship was the Boeing 247 airliner. Considered one of the first modern airliners, the 247 entered service for United in 1933. The plane's all-metal construction, retractable landing gear, and fast speed placed it far ahead of the competition.

In 1930, Boeing Air Transport, the predecessor to United, introduced the world’s first airline stewardesses.

BAT also made progress in the realm of passenger service. In 1930, the airline began what was considered to be a daring experiment. In order to ease the public's fear of flying, BAT hired Ellen Church and seven other nurses to work as stewardesses on their flights. The addition proved to be a tremendous success for the airline - BAT's flights were packed. Within a few years, most airlines followed BAT's lead in hiring nurses as stewardesses.

In 1934, a scandal erupted over how the former Postmaster General had granted air mail routes to the nation's biggest carriers. The Roosevelt administration canceled all contracts for those airlines which had benefited under the arrangement and passed new antitrust legislation. As a result, the government forbid airlines and aircraft manufacturers from being owned by the same company. With aviation holding companies forced to break apart, BAT would have to survive on its own. Boeing Air Transport, thus, became United Air Lines.

From early in its existence, United has been a leader in improving safety in aviation. In the 1930s, the airline began a research laboratory which invented such technological advancements as terrain avoidance indicators and instrument landing systems. Both developments improved flying safety. When it comes to its business decisions, United has been one of the more conservative airlines. For instance, before purchasing a fleet of jets in the late 1950s, United conducted a year-long study to learn the economic effects jet travel would have on its airline operations.

United remained almost exclusively a domestic airline for several decades. But in the mid-1980s and early-1990s, the airline broke into the international market. A financially-troubled Pan Am sold its fabled Pacific Division to United in 1985. In 1990, United added several European destinations, and a year later, Latin American routes.

United hasn't been immune from the difficulties experienced by much of the aviation industry. Embroiled in intense labor negotiations in late 1993, management offered employees company stock in exchange for salary and benefits compensation. The following year, United's 54,000 employees became part the world's largest majority employee-owned company.

Seeking to bolster its market share in the current marketplace, United announced in 2000 its plans to buy out the nation's sixth largest carrier, U. S. Airways. If approved by government antitrust authorities, the merger would make United the nation's largest airline.