WILLIAM STEPHENS, who has died aged 88, was an aeronautical scientist responsible for Britain's post-war development of Intercontinental Ballistic Missile (ICBM) technology, guided weapon systems and space launch vehicles.
Having built a considerable reputation in his field after joining the Royal Aircraft Establishment, Farnborough (RAE) as an aerodynamicist in 1935, Stephens's career prospered until, in 1959, he went to the Ministry of Aviation where he was appointed director general, ballistic missiles and Army guided weapons.
From the mid-1950s onwards Stephens had been involved in the development of Blue Streak, a long-range, liquid-propellant ballistic missile. His expertise - and the high regard in which he was held by American officials and aerospace industry scientists - greatly facilitated Britain's arrangement of technical agreements with the US government and individual American aerospace companies.
At the Ministry of Aviation Stephens remained primarily responsible for the Blue Streak strategic missile development programme until 1960, when the government of the day abandoned its development for military use.
Intelligence sources had advised Harold Macmillan's government that the Soviet Union was capable of making a pre-emptive strike with its own ballistic missiles against Blue Streak's proposed launching sites in East Anglia. This threat was exacerbated by the fact that the liquid fuel system of Stephens's rocket required some 20 minutes preparation before it was ready for use; nor could it maintain that state of readiness for extended periods.
Fortunately, Stephens was inured to the vagaries of government decisions by long experience, and he accepted disappointments in the calm, controlled and philosophical manner which always characterised his approach to his work. A dry sense of humour also helped.
Subsequently, however, Stephens's patience was rewarded, and he was much relieved when it was decided to adapt Blue Streak as the basis of a European space launcher for placing satellites in orbit.
The consequence was that in 1962 Stephens's immense contribution to the design, construction and development of Blue Streak and rocketry expertise was recognised in his appointment as technical director and deputy secretary general of the European Launcher Development Organisation (ELDO).
It gave Stephens much satisfaction when, in September that year, Blue Streak survived a flawless static test at the Spadeadam rocket site in Cumberland and was declared ready for its first live flight at the Woomera rocket range in Australia.
This successful firing reassured Stephens that nothing had been lost in the two years between cancellation of Blue Streak in its military role and the signing of the ELDO agreement. Rather, the lapse of time had permitted improvements and the achievement of greater reliability.
William Henry Stephens - always known as Bill - was born on March 18 1913 at Kilkenny, Ireland, and educated at the Methodist College and Queen's University, Belfast, where he gained Firsts in Mathematics and Mathematical Physics.
After working on aerodynamic research at RAE, Stephens moved in 1938 to the War Office's ballistic research laboratory at Woolwich where he was introduced to the then shadowy world of rocketry.
When war came in 1939, Stephens was engaged at the Air Ministry on air defence studies and system analysis. He very soon became noticed, and in 1943 was assigned to the technologically important post of assistant scientific attache to the British scientific mission in Washington.
For the next three years Stephens assiduously liaised with American scientific officials and individual company research and development teams, building contacts and friendships which were to remain fruitful and enjoyable for many years.
After returning to Farnborough in 1947, Stephens took charge of the guided weapon assessment group and after 10 years become RAE's deputy director (equipment).
Following his Blue Streak and ELDO periods, in 1969 Stephens returned to Washington where, in the rank of minister, he headed defence research and development staff at the British Embassy.
In the early days of the space shuttle programme his views were welcomed by American scientists in the field and Stephens proved effective in exploring opportunities for British companies who wanted the chance to participate.
Stephens returned to London in 1972 and was appointed special adviser on international affairs in the research controllerate at the Ministry of Defence. In 1973 he left government service for the world of business and launched General Technology Systems as a founder director.
Developing the company as a consultancy group, Stephens provided studies for a variety of clients in government and industry, as well as international organisations involved in the fields of energy conservation and new energy sources, particularly solar.
He also investigated the implications of technology advances for defence and related projects in the marine and space areas. Stephens did not retire finally from the business until 1987.
Stephens was a Fellow of the Royal Aeronautical and British Interplanetary Societies, and a member of the International Academy of Astronautics as well as of the American Institute of Aeronautics and Astronautics. He was a prolific writer of scientific papers, contributing regularly to the RAE's Journal and to other influential publications in his field. He was appointed CB in 1961.
He married, in 1938, Margaret Brown. They had a daughter who died in 1973, and a son.