Boeing was pressed into service during World War I, and would continue as a military supplier throughout its history. After WWI, there was little demand for airplanes, so Boeing resorted to producing woodwork products. Fortunately for Boeing, the advent of airmail increased demand for planes in the 1920s. With the introduction of its lightweight Model 40A in 1927, Boeing secured the San Francisco to Chicago airmail route. Slowly, but in increasing numbers, passengers started to gain the courage to take to the skies. Boeing found tremendous passenger success with the introduction of its latest model, the 247, notable because of its all-metal construction.

To run its burgeoning passenger service, Boeing Air Transport - a predecessor to United Airlines - was created. In 1929, Boeing consolidated its operations into a huge holding company called United Aircraft and Transport Company. It was a vertically integrated company with many divisions: airplanes, airlines, airmail service, engines, propellers and airports. But it would last only until 1934, when the federal government broke-up holding companies on anti-trust grounds. Boeing decided to return to its roots as a manufacturer of aircraft.

As airlines started to span entire oceans, very large transports were required. Boeing introduced its mammoth 314 flying boat in 1939. Known more commonly as one of Pan Am's Clippers, the Boeing 314 would fly passengers across the Pacific and the Atlantic in commercial service. Military application for large aircraft was required when the United States entered World War II in 1941. Development of large bombers such as Boeing's B-17 and B-29 would lead, in turn, to post-war commercial application in planes like the Stratoliner 307 and the Stratocruiser 377. The cabin of the Stratoliner 307 was the first to be pressurized, enabling smooth, high-altitude flight. Harkening back to the luxury accommodations of the flying boats, the 377 featured a lower-level lounge accessed by a spiral staircase.

Pan Am’s Juan Trippe strongly encouraged Boeing’s development of a commercial jetliner, the 707.

When the jet engine was developed during World War II, it was met with little enthusiasm in the commercial market due to its high cost of implementation. When Pan Am's Juan Trippe encouraged the industry to enter the jet age, Boeing and its main rival, Douglas, raced to introduce the first jetliner. Boeing took the lead with its four-engine 707, which entered commercial service for Pan Am in 1958. The smaller-capacity models 727 and 737 followed in the 1960s and would become mainstays in commercial fleets around the world.

To compete with the Anglo-French Concorde, the U.S. government in the 1960s funded support of an American-produced Supersonic Transport (SST). Boeing beat out Lockheed for the government contract, but was forced to cancel development in 1971 when Congress ended funding of the SST due to environmental and economic concerns.

Pan Am again pressured a reluctant airline industry when it requested production of the world's first jumbo jet, the 747. Development of the 747 strained the company's resources. When recession hit the aircraft industry especially hard in the 1970s, Boeing and its hometown Seattle were brutally hit. A billboard grimly requested that the last person leaving Seattle should turn out the lights. Boeing persevered into the 1980s and managed to outlast one of its main competitors, Lockheed, which quit the commercial aircraft business in 1983. Another of its rivals went away when Boeing acquired McDonnell Douglas in 1997.

Today, Boeing's commercial aircraft division faces serious competition from only one other manufacturer - the European consortium Airbus Industrie. While Airbus seems to be taking the lead in the area of high-capacity aircraft with its double-decker jumbo jet, the A380, Boeing is countering by developing an aircraft able to fly over .95 Mach and over distances of 11,500 miles.