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The man behind the mushroom cloud
by Michael Newland
William George Penney (later Lord Penney) was one of those practical patriotic Englishmen whose
achievements are largely in eclipse at present in the atmosphere of cynicism and self-abasement which
has been fed to a generation by liberal opinion in Britain.
Politicians and thinkers of note are reasonably assured of their place in history in the long run.
The cyclicality of ideas usually leads to rehabilitation, whatever the ill- fortune of reputations in the
shorter run. Scientific achievement, however, tends to be taken for granted once it is in place. Penney
was not only a scientist but also one who, as he was well aware, achieved something lauded at the time,
but almost guaranteed to ensure a degree of bad odour in different circumstances. Penney built Britain’s first atomic bomb.
Atomic weapons have largely disappeared from public debate in Britain since the end of the
Cold War. Viewed as unusable or without purpose in the more harmonious Europe of the 1990s,
matters looked very different in 1946 when Clement Attlee’s Labour government ordered the
development of the British bomb.
Britain still saw itself as both a great power and as the victor in the very recent hostilities. Suez
with its corrosive effect on national confidence was a long way ahead. The United States had both built
its own bomb and used it (as opinion at the time condoned) to bring World War II to an end without
massive loss of Allied lives in an invasion of Japan. Britain needed its own bomb, both to signal its
status in the world and for its deterrent effect when other countries, viewed as less friendly to Britain
than America, developed their own nuclear arsenals. The only possible defence would be the threat of
That day was nearer than was believed likely in 1947, when Penney somewhat reluctantly agreed
to head the project to build a plutonium implosion bomb of the kind dropped on Nagasaki after testing
at Los Alamos in 1944. The USSR was able to build its own bomb before long, with far from
insubstantial assistance given by the legion of naive traitors who were taken in by the communist
The war years led to an absurd overestimation of the United States’ willingness to treat Britain
as a valued friend. The ‘special relationship’ did not extend to offering the secrets of how to make the
bomb to the British government after the war. Britain had to repeat for itself much of the vast research
and development work that had gone into the Manhattan Project.
Britain, however, did not have to begin quite from square one. British scientists, including
Penney, had worked at Los Alamos, and the inevitable ‘talking shop’ within the scientific community
had eroded to a degree the complete secrecy which the US would have liked to impose. Added to this
was the great advantage Britain enjoyed in knowing that a bomb could be made and would actually
work. Furthermore, the Soviet ‘atom spies’ of the period were something of a two-edged weapon,
dispensing information to both east and west.
Penney came to what later would be known as the nuclear arms race as the result of his
volunteering for war work as a scientist. His real love was mathematics and pure research in physics.
As a recognised prodigy at Imperial College he was set for a distinguished academic career until the
war intervened. His father was a sergeant-major in the Ordnance Corps, so patriotic duty was second
nature to him, but Penney described himself later as having to be ‘dragged’ into atomic bomb work.
During the early part of the war Penney worked on blast waves under water, something of
intense practical importance in designing ships and torpedoes. It was this specialism which led to him
being sent to New Mexico in 1944 to join the group of British scientists working on the US bomb. The
key to building the plutonium bomb was designing explosive charges that would evenly compress a
sphere of the man-made material from the outside and lead to an atomic explosion. Penney joined the
group of scientists of whom Robert Oppenheimer said that they had ‘known sin’ when the test weapon
went off on 16th July, 1945 - the first nuclear explosion. He also watched from the air with Leonard
Cheshire when the bomb was used at Nagasaki.
Britain’s bomb project began in earnest in June 1947 at the library within Woolwich Arsenal,
when Penney announced to his team what the group were to do and gave a two-hour talk on the
principles of the bomb.
The problems were formidable.
Simply getting enough staff was problematical despite the priority given by the government to
the job. The Civil Service gave way to no man where bureaucratic niceties were concerned. Next there
was making sufficient plutonium to reach the critical mass needed for an explosion - about twelve
pounds. This task was given to Windscale and took years. Then there was designing, making and
testing high explosive charges that were correctly shaped and detonators that would compress the
plutonium evenly. This job was split between Woolwich Arsenal, a military establishment called Fort
Halstead near Knockholt and a firing range at Foulness. One test explosion broke windows on
Southend Pier. The whole final assembly was five feet in diameter and weighed several tons.
The project mushroomed in size as the years rolled by and moved in 1951 to a new factory at
Aldermaston, before long the focus for marches against nuclear weapons.
Penney was a big bespectacled man, eminently calm, straightforward and approachable. These
qualities were needed to deal with the endless difficulties and ghastly risks and frights involved in
building the bomb.
The plutonium bomb core was about the size of a grapefruit and came in two gold-plated halves.
On one occasion at Aldermaston one half stuck to a rubber surface as the result of its natural warmth. A
cold air blower freed it. Testing installation of the core into the explosive assembly was a job for those
with steady nerves. Two people had died at Los Alamos as the result of sudden radiation releases.
Someone was given the job of watching radiation counters and pulling a curtain ring on a piece of
string leading to a catch which could drop the parts away from one another. Public houses near
Aldermaston hosted celebrations by those who were relieved to be still alive.
No-one died and by 1952 all the parts of the bomb were ready to take to the Monte Bello Islands
in Western Australia for testing. After six years of Penney’s guiding hand, Britain became a nuclear
power on 3rd October, 1952.
Penney went on to build Britain’s hydrogen bomb, which was first tested in 1957 and later returned to
Imperial College as rector. Lord Penney died in 1991, an Englishman from a generation who enjoyed
for most of their lives freedom from being assailed by the mentality which dictates that to be British is
always to be wrong.
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