Italy had invaded Egypt in September 1940 with overwhelming numerical superiority: nine divisions, roughly 215,000 men in Libya against a British force of perhaps 36,000. The 10th Army pushed cautiously along the Mediterranean coast from the frontier, occupying Sidi Barrani before halting in mid-September to build a chain of fortified camps along an arc stretching from the sea to the inland escarpment. Then the advance stopped. Marshal Rodolfo Graziani, commanding in Libya, waited for supplies, road repairs, and a water pipeline from the frontier. The British watched, patrolled aggressively with the 7th Armoured Division, and noted something crucial: the Italian camps were spaced too far apart for mutual support. General Wavell, commanding in the Middle East, told his subordinate Lieutenant-General Richard O'Connor to plan what was intended as a five-day raid. If it succeeded spectacularly enough, they might consider extending operations.

Operation Compass launched before dawn on 9 December 1940 with meticulous deception. Fleet Air Arm Swordfish dropped flares over Maktila on the coast while ships bombarded Sidi Barrani. Inland, the real blow fell on Nibeiwa camp, where the Italian Maletti Group -- named for its commander, General Pietro Maletti -- woke to find Matilda infantry tanks grinding through their perimeter from an unexpected direction. The Matildas proved nearly invulnerable to Italian anti-tank rounds; gunners fought with rifles and hand grenades against machines they could not penetrate. General Maletti was killed leading a counterattack in his pajamas. By the time the camp fell, thousands of Italians were marching into captivity. The attacking force wheeled north to the Tummar camps and repeated the performance. The 4th Indian Division and 7th RTR, operating with precise coordination of tanks, infantry, and artillery, dismantled the Italian defensive chain one fortification at a time.

On 10 December, British armor cut the coast road between Sidi Barrani and Buq Buq, trapping the Italian garrison. The town was defended by two Italian divisions in eight strongpoints along a perimeter too long for effective command. A dust storm reduced visibility to yards, creating a surreal battlefield where tanks appeared and vanished like ghosts. The 16th Infantry Brigade attacked without waiting for artillery support and was initially repulsed by Italian fire. Three hours later, reinforced by Matilda tanks, RAF aircraft, naval gunfire, and heavy artillery, the brigade attacked again. The fighting ground on through the morning until, suddenly, two Blackshirt strongholds on the western perimeter surrendered en masse. The collapse spread. By evening, the last ten operational Matildas drove into the western defenses through blinding sand, Italian guns proving useless against their armor. Approximately 2,000 defenders, seemingly preparing to counterattack, instead threw down their weapons and gave themselves up.

The scale of the victory exceeded anything the British had imagined. From 9 to 11 December, they captured tens of thousands of Italian prisoners -- twenty times the number planned for. The prisoner columns overwhelmed the logistics system, consuming supplies and transport capacity meant for pursuing the retreating enemy. Italian casualties included 47 officers and 2,147 men killed and 78 officers and 2,208 men wounded. While retreating from Sidi Barrani and Buq Buq, 10th Army divisions crowded onto the single coast road and were pounded by naval gunfire through the day and most of the night of 11 December. By late on 12 December, the only Italian positions remaining in Egypt were at the approaches to Sollum and near Sidi Omar.

What had been planned as a five-day raid became one of the most lopsided campaigns in modern military history. O'Connor pushed westward, capturing Bardia and then Tobruk, and finally trapping the remnants of the entire 10th Army at Beda Fomm in February 1941, south of Benghazi. The campaign destroyed an army of over 100,000 men at minimal cost and captured Cyrenaica. But the very completeness of the victory contained the seeds of future setbacks: Churchill, emboldened, diverted forces from the desert to Greece, leaving the Western Desert Force dangerously weakened just as Hitler dispatched Erwin Rommel and the Afrika Korps to rescue his Italian ally. Within weeks of Beda Fomm, the British would be fighting for survival on the same ground they had just conquered. Sidi Barrani, the little Egyptian port where it all began, reverted to the obscurity from which three days of December combat had briefly lifted it.