The Russian Navy has raised its St Andrew's flag on the Ukraine Navy's only submarine, Zaporizhzhia, based in Sevastopol, Crimea, on Saturday.
Commissioned in 1970, Zaporizhzhia will be relocated to Yuzhnaya Bay to join the Russian Black Sea Fleet's three submarines.
Black Sea Fleet submarine flotilla commander captain 1st Rank Anatoly Varochkin said that half of the crew of the Zaporizhzhia, including the captain, declined to serve the Russian Navy and left the vessel.
"Half of the submarine's crew is ready to serve [Russia] and fulfill their tasks. They know their vessel and will continue service."
Russian flags were raised on approximately 190 military units in Crimea, while units also applied to join the Russian armed forces.
Meanwhile, a decree to ratify the treaty was signed by the Russian President Vladimir Putin on Friday, providing for the reconsolidation of the Crimean Peninsula with Russia.
Putin signed a decree to make Simferopol the capital of Russia's new federal district of Crimea.
Ukrainian Prime Minister Arseniy Yatsenyuk said that the government has decided to fund an additional UAH6.8bn ($697m) for defence spending to mobilise troops, modernise weapons and improve the operational capacities of the country's armed forces.