The aftermath of war

Cairncross knew about Enigma, the cipher machine used by German submarines and field units, but like many people at Bletchley he knew nothing about Colossus breaking Lorenz – and neither did the Russians. But after the war, when electronic brains were discussed even in popular newspapers, surely the Russians would realise Lorenz could be cracked?

Sale points out that the Lorenz cipher was very powerful. Some of the methods Bletchley used to crack it were not declassified until five years ago. It was a million times stronger than the Enigma ciphers, and they too were very strong.

“A couple of years back someone found in the archives three unbroken [Enigma] U-boat messages. No context. None of the clues that were used at Bletchley. The only way to break it was by a brute-force attack. A gentleman in Belgium tried it using 2,500 computers linked over the internet. It took three months.”

Still, British reticence about Colossus seems excessive. Compare what happened in the US, where the decimal 18,000-valve Electronic Numerical Integrator and Automatic Computer (Eniac) was completed in 1945, initially to perform artillery calculations. The team who built it held a series of open lectures in Philadelphia where there was a free exchange of information.

Among those attending was Maurice Wilkes, who learned enough to return to Cambridge University and build the first operational computer Edsac. This in turn formed the basis of the groundbreaking Lyons Leo, the first proper business computer.

No-one could talk about Colossus in the UK until the late 1970s – PCW (December, 1978) carried what may have been the first in-depth article about it. Sale knew about it, though. He learned about Bletchley from Peter Wright, the ex-MI5 man who became world famous when the Government tried to ban his memoir Spycatcher.

Sale was 14 at the end of the war, too young for Bletchley but not too young to have built himself a radio and a TV. He was a radar instructor with the RAF at the age of 19 and spent five years as a research assistant at Marconi before joining MI5 as a scientific officer. He describes Wright as “a lovely man”, albeit having a tendency to see communists under every bed.

Wright tells in Spycatcher of how MI5 agents allegedly bugged the Government and plotted to overthrow Prime Minister Harold Wilson. Sale left MI5 in 1963, before all that happened, and set up a succession of IT businesses until 1989, when he became manager of the computer-restoration project at the Science Museum.

While he was there he heard that Bletchley Park, now used as a training centre by BT, might be sold off to be redeveloped as a housing estate. He joined a successful campaign to save it, and turn it into a museum, then launched a project to rebuild Colossus.

He and his wife Margaret put up much of the original funding; they still work as a team, he doing the techie work and she the administration. First Sale had to collect all the information available about Colossus. This amounted to eight wartime photographs, information available from US archives, and fragments of circuit diagrams illicitly copied by engineers – now pinned on the wall behind the rebuilt Colossus.

He also had volunteer help and the memories of surviving members of the original Colossus team. It helped that Sale had learned electronics in much the same era. “Valve electronics was in my blood so I was able to put myself back into the mindset of the designers,” he said.

Tommy Flowers attended the unveiling of the first stage of the rebuild in 1996, just two years before he died. This was based on Colossus Mark 1, but limited to processing just two bits of the two five-bit data streams involved in the decipherment. The fully rebuilt Colossus Mark 2, more versatile and processing all five bits, was unveiled last year.

One of the few parts surviving from the original is an old Post Office transformer used to drive valve heaters, drawing up 1.2amps at 4v. Colossus draws around 5kw, and generates a lot of heat.
It differs in one respect from the wartime version, which was never switched off.

Sale installed a mechanised Variac (variable transformer), as used in post-war valve computers, which slowly increases or decreases the heater voltage when the machine is switched on or off. This minimises the heat stresses that caused valves to blow, earning them the reputation for unreliability that fuelled much of the early scepticism about electronic logic.

Sale points to a valve, one of 40 of wartime manufacture used in the rebuilt Colossus, to show how wrong the doubters were. “Look at that,” he said. “Still going after 64 years.”

Read the first and second parts in our retro news series.