The Soviet Red Army fought against the rebels in the fortress of Kronstadt on Kotlin Island in the Gulf of Finland, and it became a hand-to-hand battle. On the morning of March 18th, the island was placed under the control of the Red Army.

　　 On the night of March 16-17, 1921, the final attack by 50,000 Soviet Red Army troops began against the uprising that had broken out on March 7 in the Russian port city of Kronstadt. Trotsky's main force of Red Army troops attacked from the south, from Oranienbaum and St. Petersburg. The garrison numbered between 12,000 and 14,000 men, of whom 10,000 were sailors and the rest infantry. The Red Army approached the fortress on Kotlin Island in the Gulf of Finland, and fighting broke out, with hand-to-hand combat. By the morning of March 18, the island was under Communist control. Hundreds of mutinous prisoners were massacred. Some of the defeated mutineers, including their leaders, escaped.

　　The crews of the battleships Petropavlovsk and Sevastopol fought to the last man, as did the cadets of the engineering school, the torpedo detachment and the communications unit. 6,528 mutineers were arrested, 2,168 (33%) were shot, 1,955 were sentenced to forced labor, of which 1,486 were given five-year sentences, and 1,272 were released. A statistical survey of the 1935-6 uprising put the number of arrests at 10,026. The families of the rebels were deported, and Siberia was seen as the only suitable place of exile.

　　The Soviet army suffered over 10,000 casualties in the attack on Kronstadt. The number of dead rebels and those shot by the Cheka and sent to the gulag is unknown. Immediately after the defeat of the mutiny, 4,836 Kronstadt sailors were arrested and exiled to the Crimea and the Caucasus. Lenin sent them to forced labor camps on April 19th. 8,000 sailors, soldiers and civilians escaped to Finland on the ice. The Finnish government later asked the Soviet Red Army to remove the thousands of bodies lying on the frozen bay.