to proceed to the Suez Canal, which helped to relieve the strain on British shipping resources. Signals intelligence The Italians had replaced their ciphers in the AOI in November 1940 but by the end of the month, the GC&CS in England and the Cipher Bureau Middle East (CBME) in Cairo had broken the new and ciphers. By 1941, sufficient low-grade ciphers had been broken to reveal the Italian order of battle and the supply situation, by the time that the British offensive began on 19 January 1941. Italian dependence on wireless communication, using frequencies on which it was easy for the British to eavesdrop, led to a flood of information, from the daily report from the Viceroy, to the operational plans of the and on the retreat from Keren. On occasion, British commanders had messages before the recipients and it was reported later by the Deputy Director Military Intelligence in Cairo, that Casualties On 16 April 1941, the authorities in the AOI signalled to Rome that had been killed, and during military operations before the surrender. Casualties among NCOs and other ranks were and (inclusive). Casualties among locally recruited soldiers were and before the surrender; the figures did not include forces on the Giuba and eastern fronts. By May 1941, of the men in the AOI available for military operations in June 1940, only the in the garrisons near Gondar and the seven colonial divisions in Galla-Sidamo remained to be taken prisoner. More casualties among the Italian and colonial troops occurred after April 1941, in the operations against Amba Alagi (3,500 casualties), Kulkaber/Culqualber (1,003 killed and 804 wounded) and Gondar (4,000 killed and 8,400 sick and wounded). In 1959, I. S. O. Playfair, the British official historian, recorded that from June 1940 to May 1941, the East African Force had casualties and or accident cases, including and cases of which fatal. The RAF lost ; the Free French Flight N° 1 lost two Martin Marylands. The lost the in the AOI when the war began and the to the region during the campaign. The Belgian suffered from all causes. Subsequent operations Guerrilla warfare Until 27 November 1941, two African divisions mopped up pockets of resistance until the last formed Italian units surrendered. From the end of 1941 to September 1943, men in scattered Italian units fought a guerrilla war from the deserts of Eritrea and Somalia to the forests and