BOOK REVIEW / No more an enigma: Codebreakers: The Inside Story of Bletchley Park - ed F H Hinsley & Alan Stripp: OUP, pounds 17.95

BLETCHLEY PARK was the place where the German ciphers were broken during the war, and here at last are the reminiscences of those who worked there. Sir Harry Hinsley chronicled its triumphs in his official History of British Intelligence, but his narrative was so impenetrably anonymous that hardly anyone who unravelled Ultra got a mention. But in editing these accounts he has at last relented. Anyone interested in the Second World War will sit up all night, and chess players and puzzle-solvers will be captivated by later chapters.

Bletchley's success depended on one word: security. The work of the brilliant mathematicians Turing and Welchman or of another key breaker, Stuart Milner Barry, would have gone for nothing if the Germans had discovered we had broken Enigma. So no one there was allowed to know the whole story. If Bletchley had a centre, it was Hut 3 where the raw Enigma messages, deciphered in huts 6 and 8, were emended, translated and evaluated. Yet although William Millward tells us what such quick-witted inmates as Jim Rose and Peter Calvocoressi were up to, he hardly alludes to the work next door in section 3L (Oscar Oeser, Jean Alington and Christine Brooke-Rose) who were responsible for deciding which ciphers should be given priority for decoding.

In another fascinating chapter Ralph Bennett tells what it was like to be duty officer in Hut 3. He had to paraphrase the Enigma translations and convert them into Ultra so that if the Germans broke our own cipher they would not identify it as an Enigma message. In the early days Bletchley 'invented' an ubiquitous spy, Boniface, who looked over officers' shoulders, memorised messages and sent them to Bletchley, who passed them on to us in Whitehall. Once, when atmospherics had made an Enigma message almost unintelligible, I remember reading at the War Office that 'source was able to retrieve from a wastepaper basket a badly charred document'. Such jocular ingenuity became impossible when Enigma decrypts rose during 1943 from 39,000 to 90,000.

Ultra was only one of the Bletchley products. Some worked on V1 and V2 ciphers, some on railway ciphers. Some searched for cribs that gave away technical secrets, others could tell from an unsigned message who sent it because they got to know the style of the operators chatting to each other. There were hand ciphers, especially the Abwehr cipher, which Dilly Knox broke. Late in the war the first true electronic computer, Colossus, enabled us to read messages sent by the German High Command to theatre commanders. The British could now get a glimpse of German strategy. The Italians, who did not have Enigma, used old-fashioned ciphers. They were far harder to break.

Not enough space is given to the women, all ill-paid and nearly all doing dull clerical jobs. Joan Murray, a cryptographer, was luckier, but bureaucratic devices stopped her being paid on equal terms with men. The worst treated were those among the 2,000 Wrens who worked the Bombes, the machines which Turing invented to determine the wheel-settings for the Enigma cipher. Year after year, with little chance of promotion, they worked whey-faced for four weeks of eight-hour shifts followed by four days' leave, getting electric shocks from the Bombes and living in hideous conditions. At one establishment, Diana Payne recalls, they had to attend morning parade and squad drill after night duty. Some collapsed, others had nightmares that they had broken security: their sole recognition was Churchill thanking 'the chickens for laying so well without clucking'.

Ultra enabled the convoys to dodge the U-boats in 1941. Then the Germans added a fourth wheel to the Enigma machine, the cryptographers could not read the traffic and the numbers of sinkings reached terrifying heights until the cryptographers once again broke the cipher. Auchinleck and Montgomery knew exactly when and where the Afrikakorps would attack; we also knew how the German High Command would oppose Overlord.

In the early days our own top brass would not believe the new source. The Admiralty was particularly oak-bottomed. When Christopher Morris deciphered a message in the spring of 1940 that ships bound for Bergen should report to the German War Office, he was told not to send nonsense: ships did not report to the army. The ships in question were, in fact, carrying troops to invade Norway. Harry Hinsley had a sixth sense in deducing from the traffic and decrypts if something was up, but was ignored when he told them of indications that heavy ships were leaving the Baltic; as a result HMS Glorious was sunk. From then on Hinsley, still an undergraduate, with an astonishing mop of hair and a cheeky smile, was welcomed by the Fleet and at the Admiralty.

Several authors accuse the army of failing to use Ultra properly - why did Montgomery let Rommel off the hook at Alam Halfa? But by design no one at Bletchley was allowed to know of Allied plans; nor how inferior our tanks were to the German panzers; nor how Monty had to retrain the Eighth Army to fight as divisions and not in battle groups; nor how some of the old desert hands commanding divisions disobeyed his orders. No wonder he would not let loose his inferior equipment when he had Alamein in mind.

Does this book tell us what it was like to work there? Yes and no. There are too few character sketches. Who were the animators, who were the bores? The marvellous camaraderie, the total informality and the contempt for anyone who tried to pull rank in this brigade of intellectual linguists and mathematicians hardly surface in this grave account. Why was not Patrick Wilkinson's droll account of the gaiety, the jokes, the scorn for the 'Other Side' - ie, the spy-masters - published? Only occasionally the excitement surfaces: when Millward translated a signal from Rommel that read: 'the panzer army is exhausted'. When memory stirs I am still Intelligence night duty officer at the War Office studying German troop movements, and the teleprinter clatters out a message from Bletchley revealing the exact route the next convoy of troops, tanks and supplies for Rommel will take; and I think: 'Will our submarines get them?' They did.