Crew of the Russian frigate Osliaba harbored in Alexandria, Virginia, 1863.
During the American Civil War, the Russian Empire was an open supporter of the Union. When Britain and France threatened to go to war with the United States in 1863, Czar Alexander II sent the entire Russian Baltic Fleet to New York City in support of the Union Navy. Britain was also threatening to intervene against Russia in the Polish Uprising of 1863, and thus it was decided the fleet would be safer in American, rather than the Baltic where it could be trapped by the Royal Navy. This act, along with Prussian threats to go to war with France in support of the Union, caused Britain and France to back off.
For six months the Russian fleet harbored along the Atlantic Coast, helping to enforce the Union blockade on Southern ports. Russian ships of the Far East Fleet also harbored in San Francisco to protect the city against Confederate raiders.