An Italian submarine torpedoes and sinks the Greek cruiser Elli at Tinos harbor during peacetime, marking the most serious Italian provocation prior to the outbreak of the Greco-Italian War in October.

The Kingdom of Italy was a unitary state that existed from 17 March 1861, when Victor Emmanuel II of Sardinia was proclaimed King of Italy, until 10 June 1946, when the monarchy was abolished, following civil discontent that led to an institutional referendum on 2 June 1946. This resulted in a modern Italian Republic. The kingdom was established through the unification of several states over a decades-long process, called the Risorgimento. That process was influenced by the Savoy-led Kingdom of Sardinia, which was one of Italy's legal predecessor states.

Elli was a 2,600 ton Greek protected cruiser named for a naval battle of the First Balkan War in which Greece was victorious. She was completed in 1913 and commissioned in 1914. Elli saw action during World War I and in the disastrous Asia Minor Expedition. An Italian submarine sank her before the outbreak of the Greco-Italian War on 15 August 1940 while she sat at anchor.

Tinos is a Greek island situated in the Aegean Sea. It forms part of the Cyclades archipelago. The closest islands are Andros, Delos, and Mykonos. It has a land area of 194.464 square kilometres (75.083 sq mi) and a 2021 census population of 8,934 inhabitants.

The Greco-Italian War, also called the Italo-Greek War, Italian campaign in Greece, Italian invasion of Greece, and War of '40 in Greece, took place between Italy and Greece from 28 October 1940 to 23 April 1941. This conflict began the Balkans campaign of World War II between the Axis powers and the Allies, and eventually turned into the Battle of Greece with British and German involvement. On 10 June 1940, Italy declared war on France and the United Kingdom. By September 1940, the Italians had invaded France, British Somaliland and Egypt. This was followed by a hostile press campaign in Italy against Greece, accused of being a British ally. A number of provocations culminated in the sinking of the Greek light cruiser Elli by the Italians on 15 August. On 28 October, Mussolini issued an ultimatum to Greece demanding the cession of Greek territory, which the Prime Minister of Greece, Ioannis Metaxas, rejected.