Hawker Siddeley much larger firms. Out of this decision, came the "order" that all future contracts being offered had to include agreements to merge companies. In 1959, Folland Aircraft was acquired, followed by de Havilland Aircraft Company and Blackburn Aircraft in 1960. In 1963, the names of the constituent companies were dropped, with products being rebranded as ""Hawker Siddeley"" or ""HS"". In this period, the company developed the first operational, and, by far, the most successful VTOL jet aircraft, the Harrier family. This aircraft remained in production into the 1990s and remains in service. In 1948, Hawker Siddeley acquired a factory in
McDonnell Douglas AV-8B Harrier II project in March 1975 owing to decreased defense funding, rising costs, and the RAF's insufficient 60-aircraft requirement. With development costs estimated to be around £180–200 million (1974 British pounds), the United States was unwilling to fund development by itself, and ended the project later that year. Despite the project's termination, the two companies continued to take different paths toward an enhanced Harrier. Hawker Siddeley focused on a new larger wing that could be retrofitted to existing operational aircraft, while McDonnell Douglas independently pursued a less ambitious, though still expensive, project catering to the needs of the US military. Using knowledge