(Oct. 17, 1854–Sept. 11, 1855), the major operation of the Crimean War (1853–56), in which 50,000 British and French troops (joined by 10,000 Piedmontese troops during 1855), commanded by Lord Raglan and Gen. François Canrobert, besieged and finally captured the main naval base of the Russian Black Sea fleet. Sevastopol's defenses had been built by the military engineer Colonel Eduard Totleben, and the Russian troops were commanded by Prince Aleksandr Menshikov. The siege lasted 11 months because the allies lacked heavy artillery to smash the defenses effectively, while all Russian efforts to break the siege failed. Winter brought on severe suffering and heavy casualties among the allied troops, whose commanders had made little or no provision for a winter campaign. This situation produced several crises within the British government. On Sept. 8, 1855, French troops took and held the Malakhov, a vital defensive position at the southeast end of the city. On September 11 the Russians sank their ships in the harbour, blew up the fortifications, and evacuated Sevastopol. The allies took the city but did not pursue the Russians. The war then moved rapidly toward an end in early 1856.