[12][13] Prince Carol I accepted the Duke's proposal to become the Marshal of the Russian troops in addition to the command of his own Romanian army, thus being able to lead the combined armed forces to the conquest of Plevna and the formal surrender, after heavy fighting, of the Turkish General Osman Pasha.

The Army won the battles of Grivitsa and Rahova, and on 28 November 1877 the Plevna citadel capitulated, and Osman Pasha surrendered the city, the garrison and his sword to the Romanian colonel Mihail Cerchez and Russian division commander Ivan Ganetsky.

After the occupation of Plevna, the Romanian Army returned to the Danube and won the battles of Vidin and Smârdan.

The Romanian Navy consisted of three gunboats: Ştefan cel Mare, România and Fulgerul and one spar torpedo boat, Rândunica.

[19] According to the Russian-Romanian treaty signed in April that year, the Romanian spar torpedo boat Rândunica served under joint Romanian-Russian command.

Rândunica was returned to full Romanian control in 1878, after the Russian ground forces had finished crossing the Danube.

[22] The Convention between Russia and Romania, which established the transit of Russian troops through the country, is one by which Russia obliged itself "to maintain and have the political rights of Romanian state observed, such as they result from the internal laws and the existent tratatives and also to defend the present integrity of Romania".

[23] The Romanians believe that "defend" in a diplomatic act means recognition of the status-quo set by Congress of Paris of 1856, whereby three counties in Southern Bessarabia (part of Budjak, a region conquered by Turks around the late 15th century and ruled until the late 19th century when it was conquered by Russians) were taken from the Russian Empire, defeated in the Crimean War, and given back to the Romanians in Principality of Moldavia.

[24][25] The treaty was not recognised by the Central Powers and the 1878 peace conference in Berlin decided that Russia would give Romania its independence, the territories of Northern Dobruja, the Danube Delta and access to the Black Sea including the ancient port of Tomis, as well as the tiny Snake Island (Insula Şerpilor), but Russia would nevertheless occupy as a so-called "compensation" the old Romanian counties of Southern Bessarabia (Cahul, Bolgrad and Ismail), which by the Treaty of Paris of 1856 (after the Crimean War) were included in Moldavia.

Prince Carol was most unhappy by this unfavorable turn of negotiations; he was finally persuaded by Bismarck (in now-published original letters exchanged at that time) to accept this compromise with Russia in view of the great economical potential of Romania's direct access to the Black Sea and its ancient ports at the expense of Bulgaria.