It is difficult to exaggerate the importance of Ultra intelligence (the information derived from decrypting the radio traffic of the German armed force).

For example, within four days of his arrival in the desert in August, 1942 Ultra told Montgomery that the new troop dispositions he had just made were ideally suited to counter Rommel''s last attempt to reach the Nile; the way was cleared for Alamein and the turning of the tide of the war. Before the invasion of Sicily in July, 1943 an Allied feint sought to baffle the German defence by suggesting that Sardinia and Greece were the targets. Hitler was duped and within three days Ultra knew that he had been and could reassure Eisenhower that the Germans were not concentrating in Sicily but were preparing to defend the whole southern European coastline.

After the assault on Italy in the following September, would Hitler waste men, tanks, petrol and guns stubbornly contesting the Italian peninsula, or would he economize resources by retiring to the Alps? By the beginning of October Ultra showed that Hitler was the unwitting accomplice of Allied policy, pouring his diminishing resources into Italy when they might have been put to better use against the Russians or against the invasion of France the following year: the knowledge was invaluable for the direction of Allied strategy for the remainder of the war.

Faber Finds are reissuing Ralph Bennett''s three Ultra titles, the other two being Ultra in the West; the Normandy Campaign of 1944-1945 and Behind the Battle: Intelligence in the War with Germany, 1939-45.