Romanian Black Sea Fleet during World War I

During World War I, the Romanian Black Sea Fleet played a significant role in defending the Danube Delta and its coast against the Central Powers. Established in 1890, the fleet consisted of several key warships, including the protected cruiser Elisabeta, the armed brig Mircea, three Smeul-class torpedo boats, the gunboat Grivița, and the minelayer Alexandru cel Bun. These vessels were largely outdated, as most were built between 1880 and 1888, unlike the modernized Danube Flotilla. Elisabeta was converted into an anti-aircraft cruiser during the war, while Mircea served as a training ship with limited armament.

The fleet's base shifted to Sulina after Constanța was leased to Russian forces and later fell to Central Powers during the Second Battle of Cobadin. Against Germany, the torpedo boat Smeul sank the German submarine UC-15 in November 1916 when it struck one of its own mines. In 1917, Smeul narrowly avoided damage from a German seaplane's bombs but managed to capture the pilot.

Against the Ottoman Empire, Smeul successfully raided enemy troops at Tulcea using her two 37 mm guns. However, on April 16, 1917, Smeul sank during a storm while transporting materials and personnel, resulting in the loss of 18 crew members, including three French officers.

The fleet's most significant success came against Austria-Hungary when Alexandru cel Bun laid a mine that sank the Austro-Hungarian monitor SMS Inn on September 22, 1917. The Inn was later salvaged but remained under repair until the war ended.