The Italian invasion of British Somaliland (3–19 August 1940) was part of the East African campaign (1940–1941) in which Italian, Eritrean and Somali forces entered the Somaliland Protectorate and defeated its garrison of British, Commonwealth and colonial forces supported by Somali irregulars. The Italian victory was based on mobility and speed but was hampered by the terrain, rainy weather and British resistance.

At the Battle of Tug Argan (11–15 August) Italian attacks had the advantage of artillery and the outnumbered defenders were gradually worn down and slowly outflanked, until the remaining fortified hilltops were vulnerable to capture. After the failure of a counter-attack towards the Mirgo Pass, the local commander, Major-General Reade Godwin-Austen, had too few men to retrieve the situation and to keep open an escape route at the same time and was given permission to retreat towards Berbera.

The British fought a rearguard action at Barkasan on 17 August and retreated after dark. The improvised evacuation went better than expected and the second blocking position at Nasiyeh was not needed. The rainy weather continued to slow the Italian advance and when the airstrip near Berbera was found still to be garrisoned, a prospective Italian coup de main was cancelled. The British defeat was controversial and the beginning of a deterioration in relations between General Archibald Wavell, the theatre commander, his subordinates and Prime Minister Winston Churchill, which ended in Wavell being superseded by Claude Auchinleck in July 1941.

On 9 May 1936, Italian dictator Benito Mussolini proclaimed the foundation of Italian East Africa (Africa Orientale Italiana, AOI), formed from the colonies of Italian Eritrea, Italian Somaliland, and Ethiopia, conquered in the Second Italo-Ethiopian War (3 October 1935 – 5 May 1936). On 10 June 1940, Mussolini declared war against Britain and France, making the Italian forces in Africa a threat to British supply routes along the Mediterranean, the Suez Canal and the Red Sea. Egypt and the Suez Canal were obvious targets and an Italian invasion of French Somaliland (Djibouti) or British Somaliland was also feasible. Mussolini looked forward to propaganda triumphs in Sudan and British East Africa (Kenya, Tanganyika and Uganda). The Italian General Staff had based its strategic calculations on an assumption that there would be no war until 1942; the Regio Esercito (Italian Royal Army) and Regia Aeronautica (Italian Royal Air Force) were not prepared for a long war, nor to occupy large tracts of Africa.

The Kingdom of Egypt included Sudan, a condominium between Egypt and Britain. The British had based military forces in Egypt since 1882 but these were greatly reduced by the terms of the Anglo-Egyptian Treaty of 1936, which only allowed British military forces to occupy Egypt in defence of the Suez Canal. The small British and Commonwealth force garrisoned the Suez Canal and the Red Sea route, which was vital to Britain's communications with its Far Eastern and Indian Ocean territories. In mid-1939, Lieutenant-General Archibald Wavell was appointed General Officer Commanding-in-Chief (GOC-in-C) of the new Middle East Command, with responsibility for the Mediterranean and Middle East. Until the Franco-Italian Armistice (Armistice of Villa Incisa), the Italian 5th Army in Tripolitania (western Libya) faced the French army in Tunisia and the Italian 10th Army in Cyrenaica (eastern Libya), confronted the British in Egypt.

The Italian Royal Army had about 215,000 men in Libya and in Egypt, the British had about 36,000 troops, with another 27,500 men training in Palestine. Wavell had about 86,000 troops at his disposal for Libya, Iraq, Syria, Iran and East Africa. Faced with frontiers guarded by about eight men to the mile, Wavell concluded that a defensive strategy was the only feasible policy and intended to mount delaying actions at the main posts and hope for the best. The Foreign Secretary Anthony Eden convened a conference in Khartoum at the end of October 1940 with Emperor Haile Selassie, the South African General Jan Smuts (an advisor for the region with Winston Churchill), Wavell and the senior military commanders in East Africa, including Lieutenant-General Platt and Lieutenant-General Cunningham. An offensive strategy was decided on against Ethiopia, including the use of Arbegnoch (Amharic for Patriots), by the conference. In November, the British and Commonwealth forces gained an intelligence advantage, when the Government Code and Cypher School (GC & CS) at Bletchley Park broke the high-grade cypher of the Royal Army in East Africa. Later in that month, the replacement cypher for the Regia Aeronautica was broken by the Combined Bureau, Middle East (CBME).

The British had fought the Somaliland Campaign (1900–1920) against Diiriye Guure and his Dervish state, to gain control over the territory. In 1910 the British garrison had been forced to retreat to the coast until the end of the First World War and only after four campaigns did Somali resistance end in 1920, after three weeks of attacks by local troops, a King's African Rifles (KAR) battalion and the Royal Air Force (RAF). The colony had an area of about 68,000 sq mi (180,000 km²) with a plain inland from the coast up to 60 mi (100 km) deep, ending at a mountain range an average of 4,000 ft (1,200 m) high.

There was little scope for agriculture and most of the 320,000 inhabitants made a living from livestock herding. Berbera, the biggest town and port, was ringed by desert and scrubland; in the cold season it had a population of about 30,000, falling to around 15,000 in the summer months. The port was a first class anchorage and was the principal entrepôt of the colony, despite having no port installations making it unsuitable for an expeditionary force, since ships had to be unloaded by lighter, a method that took ten days to empty a 3,000 gross register ton (GRT) ship. Loading and unloading was impossible during the period from July to August, when the Kharif, a strong and hot wind, blew.