Belgo-Congolese troops, British Commonwealth forces and local resistance fighters besieged the fort at the market town of Saïo in south-western Ethiopia in 1941.

Almost no fighting took place in May as heavy rain bogged down the Belgians and turned their supply line from Sudan into mud, creating a food shortage.

Aggressive patrols, combined with the actions of the Ethiopian resistance and raids from the South African Air Force put increased pressure upon the Italian garrison.

Italian belligerence also closed the Mediterranean to Allied merchant ships and endangered British supply routes along the coast of East Africa, the Gulf of Aden, Red Sea and the Suez Canal.

[3] Amedeo, Duke of Aosta, was appointed Viceroy and Governor-General of Italian East Africa in November 1937, with a headquarters in Addis Ababa, the Ethiopian capital.

[4] On 10 June, the Regio Esercito (Italian Royal Army) was organised in four commands, with the military forces in Ethiopia led by General Pietro Gazzera.

[5] In August 1939, Field Marshall Archibald Wavell, C-in-C Middle East ordered a plan covertly to encourage a rebellion in the western Ethiopian province of Gojjam, which the Italians had never been able entirely to repress after the end of the Second Italo-Ethiopian War in May 1936.

Sandford requested that supply routes to the area north of Lake Tana be established before the rains ended and that Selassie should return in October as a catalyst for the uprising.

Gaining control of Gojjam required the Italian garrisons to be isolated along the main road from Bahrdar Giorgis south of Lake Tana, to Dangila, Debra Markos and Addis Ababa, to prevent them concentrating against the Arbegnoch.

Mission 101 managed to persuade the Arbegnoch north of Lake Tana to spring several ambushes on the Metemma–Gondar road and the Italian garrison at Wolkait was withdrawn in February 1941.

Governor-General Pierre Ryckmans was forced to send a senior member of his staff to calm them down and explain the importance of the Congo's economic contribution to the war.

[9] Meanwhile, Ryckmans and Lieutenant General Paul Ermens discussed the possibility of sending an expedition to Italian East Africa with the South African and British military missions in Léopoldville.

[12] Free French Forces consolidated their control over Equatorial Africa at the Battle of Gabon and more German involvement in the Balkan Campaign (begun by Italy in 1939) made the possibility of intervention in Portugal remote.

The expeditionary force took the Vicicongo line (a narrow-gauge railway) from Aketi to Mungbere and drove by lorry to Juba in Sudan where they took to the White Nile.

After a series of actions in 1940, British colonial forces from Anglo-Egyptian Sudan invaded the territory and eventually a salient formed around the Baro River.

[14] Next, the Belgians and Congolese began attacking the town of Gambela directly from the west while two companies of the 2/6 KAR under Captain J. W. E. Mackenzie were sent to outflank it and cut off its link with the Italian headquarters at Saïo[15] under the command of General Carlo De Simone.

[20] Instead they made moves to contain the Italian forces around Saïo from the west, while British troops under General Alan Cunningham conducted operations in Somalia and eastern Ethiopia.

A Belgian sergeant caught three Italian officers at gunpoint but lowered his revolver when they claimed to be English, thinking the KAR might have dispatched a liaison party to the area.

[25] During the ensuing stalemate, the Belgians studied the Italians' tactics; they would post pairs of snipers and artillery spotters in trees guarded at the bases by infantry squads.

After a two-hour bombardment, Eritrean troops armed with automatic weapons and hand grenades and covered by Galla snipers penetrated the Belgians' left and right flanks.

[25] With Van der Meerch's battalion suffering the brunt of the assault, the Belgians retreated behind a pair of hills that obscured them from Italian observers, which the latter then seized.

The Baro and Sobat rivers were still too low to permit the passage of supply barges from the White Nile and the nearby Gambela airfield was too small for transport aircraft to land.

[22] At the regular front, Lieutenant Colonel Dronkers-Martens ordered his troops to increase their patrol activities upon the Saïo Plateau, to make the Italians believe that they were facing superior forces.

Eventually the South African Air Force (SAAF) committed three Hawker Hart biplanes to regularly bomb the Saïo fortress and strafe the surrounding roads.

[29] On 27 June Lieutenant General William Platt, advancing with British forces from Sudan, ordered the Belgians to attack the Italian positions if an opportunity presented itself and Gilliaert immediately undertook preparations for an offensive.

[29][32] I based our chances of success upon continuously keeping aggressive activity along Bortai Brook against Mogi and applying Kitchener's maxim that you can try anything against an enemy who refuses to budge himself.Believing the British pursuit to be closer than it actually was, Gazzera ordered the bridge over the Indina River 40 mi (64 km) east of Saïo to be blown, thereby trapping his forces.

[33] The Belgians captured the hills and the Italians, being flanked on their left side by Van der Meersch's troops, were unable to make it back to their fortifications atop Saïo mountain.

[32][19] At Gazzera's request, Gilliaert guaranteed the Eritrean Askari safe passage to British prisoner of war camps in the east and sent Congolese guards to protect them from Ethiopian retaliation.

A total of 6,454 Italian troops were taken prisoner, including Gazzera, eight other generals and 3,500 Askari, along with 20 artillery pieces, 200 machine guns, 250 trucks and 500 mules.