the sand sea. Scorpions, vipers and flies populated the region, which was inhabited by a small number of nomads. Bedouin tracks linked wells and the more easily traversed ground; navigation was by sun, star, compass and "desert sense", good perception of the environment gained by experience. When Italian troops advanced into Egypt in September 1940, the Maletti Group got lost leaving Sidi Omar and had to be found by aircraft. In spring and summer, days are miserably hot and nights very cold; the Sirocco (Gibleh or Ghibli), a hot desert wind, blows clouds of fine sand, which reduces visibility to a few metres and coats eyes, lungs, machinery, food and equipment; motor vehicles and aircraft need special oil filters and the barren ground means that supplies for military operations have to be transported from outside. German engines tended to overheat and tank engine life fell from to , which was made worse by the lack of standard parts for German and Italian types. The ground is a hard surface which drops to sea level in steps, with the coast cut by ravines. The Italian fortifications at Tobruk included an outer perimeter, comprising a double semi-circle of dug-in strong points with concrete walls, positioned well for forward observation, an inner anti-tank ditch, some parts of which were behind barbed wire and/or included booby traps, as well as several more fortified positions closer to the port, at the Bardia–El Adem road junction and towards Fort Pilastrino. Capture of Tobruk The British captured Tobruk from the Italians in January 1941. Prelude Operation Sonnenblume In February 1941, the Allies defeated the 10th Army and the 5° of the Regia Aeronautica, after which Allied leaders decided to hold the area with minimal forces and send the remainder of the WDF to Greece. The Australian 9th Division and the British 2nd Armoured Division (Major-General Michael Gambier-Parry), minus a brigade group sent to Greece, were left to garrison Cyrenaica under Cyrenaica Command (Cyrcom: Lieutenant-General Henry Maitland Wilson), despite the inadequacy of the force if the Germans sent reinforcements to Libya. Command in Egypt was taken over by Lieutenant-General Richard O'Connor and the XIII Corps HQ was replaced by the HQ of the 1st Australian Corps (Lieutenant-General Thomas Blamey). It was believed by Wavell and the GHQ in Egypt that the Germans could not attack until May, when the 9th Australian Division, two more divisions and support troops,