Hawker Siddeley, one of the largest and best-known companies in British aviation, got its start through a bankruptcy. The failed firm, Sopwith Aviation, had been very active during World War I and had built the famous Sopwith Camel fighter plane. Orders from the government dried up following the end of the war, in 1918, and Sopwith found itself struggling. Then the British treasury presented a very large bill for excess profits during the war. Unable to pay it, Sopwith responded by declaring that it was bankrupt. Its assets were taken over by a group of investors led by the test pilot Harry Hawker. His new firm, H. G. Hawker Engineering Company, opened for business late in 1920.

Hawker found work initially by building motorcycles and motorcars and by rebuilding used aircraft. However, company officials wanted to return to being full-time planebuilders. The Royal Air Force was placing orders for small numbers of new aircraft from a variety of British companies, which gave Hawker Engineering its opportunity. A brilliant chief designer, Sydney Camm, helped as well.

Under his leadership, Hawker scored a substantial success with a single-engine bomber, the Hart. Camm introduced a steel framework for light weight. The finished aircraft had an empty weight of only 2,530 pounds (1,148 kilograms), which gave it great speed. When the first Harts entered service in 1930, they had a top speed of 184 miles per hour (296 kilometres per hour), which was 30 miles per hour (48 kilometres per hour) faster than biplane fighters that tried to intercept.

The Hart remained in production through much of the 1930s, and gave rise to 17 variants. Because of its high speed, it was adapted for use as a fighter. Another version, fitted with pontoons, flew with aircraft carriers of the Royal Navy. More than 3,000 Harts were built, making this the most produced British airplane in the years before World War II.

Few other companies approached this success. Indeed, after 1930, the Great Depression placed many planebuilders under considerable financial stress. Officials of the British government responded by encouraging aviation leaders to reorganize their industry into fewer but stronger companies. Thomas Sopwith, chairman of Hawker, took the initiative by drawing on profits from sales of Harts as he raised capital of £2 million, some $10 million. He then bought up other firms: Gloster Aircraft, Armstrong Siddeley Motors, Armstrong Whitworth Aircraft, Air Service Training, and A. V. Roe. In 1935 he reorganized these holdings as the Hawker Siddeley Aircraft Company. These mergers placed those firms on a good financial footing, at a time when war was only a few years away.

Also during 1935, the rising threat of war with Germany led the Under-Secretary of State for Air, Sir Philip Sassoon, to announce a sharp increase in the purchase of warplanes. This change in policy took place at a time when aircraft design was changing dramatically. The best aircraft of the day, including the Hart, still were biplanes. However, by the mid-1930s the all-metal monoplane was in the forefront. Such aircraft were heavier than biplanes, but excellent streamlining made them considerably faster. At Hawker, Sydney Camm soon was ready with a new fighter: the Hurricane. It first flew in November 1935. In April 1936, the directors of Hawker placed it into production even before receiving a formal government order. It entered service in 1938 and showed a top speed of 325 miles per hour (523 kilometres per hour), nearly twice that of the Hart.

Then in April 1940, the dictator of Germany, Adolf Hitler, unleashed a powerful army that already had overrun Poland in less than a month. The Netherlands now fell in only five days. France surrendered in June. With complete victory in view, Hitler then ordered his generals to prepare to invade England. Only one military command stood in their way: the Royal Air Force.

The ensuing Battle of Britain succeeded in defending that nation, as Hitler called off his invasion. The Hawker Hurricane emerged as the outstanding fighter of this conflict. Hurricanes in service outnumbered all other British fighters combined, shooting down 55 percent of all enemy aircraft destroyed. The historian Francis Mason writes that the Hurricane showed superior "ability to withstand battle damage, ease of repair, better ability to operate from poor quality [airfields] and comparative ease of flight training. It also proved much simpler to fly at night."

The end of World War II led quickly to the Cold War, a prolonged confrontation with the Soviet Union. Jet engines now were the key to fighter design, and Sydney Camm took advantage of their power by developing the Hawker Hunter fighter-bomber. During an early flight in 1953, its test pilot set a world speed record of 728 miles per hour (1,172 kilometres per hour). Amid steady improvement, the Hunter was crafted in 12 versions, with some 2,000 of these aircraft being built by 1960. Faster fighters by then were available, but a Hunter could be refuelled and rearmed in as little as five minutes. It found a particular role in attacking ground targets, for which it did not require supersonic speed. It became popular in the export market, with hundreds of Hunters remaining in service into the 1980s.

Even so, it was clear by the mid-1950s that modern aircraft were too costly for Britain to pursue on its own. Nor was there need for them; American warplanes were the world's best and could easily be purchased. In 1957 the British minister of defence, Duncan Sandys, issued a White Paper, a formal document that announced a new policy: Great Britain would build no new fighter aircraft for its Royal Air Force. The industry was free to build airliners, sell fighters overseas, and collaborate with the United States and with France. Even so, this policy brought a sharp cutback in the prospects for Britain's planebuilders.

They responded with a new wave of mergers. The engine-builders Armstrong Siddeley and Bristol Aero-Engines combined in 1959 to form Bristol Siddeley. Hawker Siddeley took over the big firm of De Havilland Aircraft in 1960. Vickers, English Electric, and Bristol Aircraft united to create British Aircraft Corporation, also in 1960. Rolls Royce, the nation's leading engine builder, merged with Bristol Siddeley in 1966.

At Hawker, innovation continued. Ralph Hooper, a senior manager, developed a strong interest in a new Bristol engine, the Pegasus, with nozzles that could swivel in any direction. Hooper saw that a fighter powered by such an engine could direct its thrust downward to take off and land vertically, to hover, to stop in midair, and to manoeuvre in flight with unprecedented agility. He built an experimental airplane, the P.1127, which first flew in 1960. This led to an operational fighter, the Harrier. It showed such promise that the British government reversed its White Paper policy and purchased Harriers for both the Royal Navy and Royal Air Force, with the first of them entering service in 1968. The U.S. Marines acquired their own Harriers. In addition, Hawker Siddeley formed a partnership with America's firm of McDonnell Douglas. This brought development of an advanced Harrier that could carry heavier loads.

The Harrier went to war in 1982, when Argentina seized the British-held Falkland Islands in the South Atlantic. Prime Minister Margaret Thatcher sent a naval force that included these fighters. They shot down 28 Argentine aircraft while losing none of their own in aerial combat. The British won the battle and took back the islands.