On 10 June 1940, the Kingdom of Italy aligned itself with Germany and declared war upon France and the United Kingdom. British forces based in Egypt were ordered to undertake defensive measures, but to act as non-provocative as possible. However, on 11 June they began a series of raids against Italian positions in Libya. In addition there had been a large Italian community in Cairo prior to the war. Following the June 10, 1940 declaration of war, nearly all of the Italian men were arrested and nearly all Italian property was seized, leaving the women in poverty.
Meanwhile following the defeat of France on 25 June, Italian forces in Tripolitania, facing French troops based in Tunisia, redeployed to Cyrenaica to reinforce the Italian Tenth Army. This, coupled with the steadily degrading equipment of the British forces led General Archibald Wavell to order an end to raiding and placed the defense of the Egyptian border to a small screening force.
El Duce Benito Mussolini ordered that the Tenth Army was to invade Egypt by 8 August. Two days later, no invasion having been launched, Mussolini ordered Marshal Graziani that the moment German forces launched Operation Sealion, he was to attack. On 8 September, Italians, hampered by the lack of transport and enfeebled by the low level of training among officers and weakened by the state of its supporting arms, were ordered to invade Egypt the following day. The battle plan was to advance along the coastal road while limited armored forces operated on the desert flank. To counter the Italian advance, Wavell ordered his screening forces to harass the advancing Italians, falling back towards Mersa Matruh where the main British infantry force was based. Positioned on the desert flank was the 7th Armoured Division, which would strike into the flank of the Italian force.
By 16 September the Italian force had advanced to Maktila, around 80 miles (130 km) west of Mersa Matruh, where they halted due to supply problems Despite Mussolini urging for the advance to carry on, Graziani ordered his force to dig in around Sidi Barrani, and fortified camps were established in forward locations; additional troops were also positioned behind the main force.
During November General Richard O'Connor was appointed an acting lieutenant-general in recognition of the increased size of his command
In response to the dispersed Italian camps, the British planned a limited five-day attack. The counteroffensive, Operation Compass, began on 8 December 1940. O'Connor's relatively small force of 31,000 men, 275 tanks and 120 artillery pieces, ably supported by an RAF wing and the Royal Navy, broke through a gap in the Italian defenses at Sidi Barrani near the coast. The Desert Force cut a swath through the Italian rear areas, stitching its way between the desert and the coast, capturing strongpoint after strongpoint by cutting off and isolating them, The Italian guns proved to be no match for the heavy British Matilda tanks and their shells bounced off the Armour. By mid-December the Italians had been pushed completely out of Egypt, leaving behind 38,000 prisoners and large stores of equipment. The attack was supported by 25 pounder (11 kg) artillery and Blenheim bombers and was centered on the advance of Mk.II Matilda tanks. Within an hour of the onset of combat, Italian GeneralPietro Maletti would be dead and 4,000 Italian soldiers would surrender. Within three days, 237 artillery, 73 tanks, and 38,300 soldiers would be captured. The attacking forces would move west along the Via della Vittoria, through Halfaya Pass, and capture Fort Capuzzo, Libya.
During January the fortified towns of Bardia and Tobruk were captured and the fleeing Italians were cut off at Beda Fomm by the 7th Armoured Division, who had crossed the western desert. At the Battle of Beda Fomm the remnants of the Italian army surrendered. Within ten weeks Allied forces had reached El Agheila and destroyed the Italian Tenth Army, taking 130,000 prisoners of war.
The British would suffer 494 fatalities and 1,225 wounded. However the advance stopped short of driving the Italians out ofNorth Africa. As the advance reached Al Argheila, Churchill ordered that it be stopped, and troops dispatched to defendGreece.
A few weeks later the first troops of the German Afrika Korps would begin arriving in Tripoli Operation Sunflower (German: Unternehmen Sonnenblume), and the desert war would take a completely different turn.