ussia has withdrawn the bulk of its Black Sea Fleet from its main base in occupied Crimea, a potent acknowledgment of how Ukrainian missile and drone strikes are challenging Moscow’s hold on the peninsula. Russia has moved powerful vessels including three attack submarines and two frigates from Sevastopol to other ports in Russia and Crimea that offer better protection, according to Western officials and satellite images verified by naval experts. The Russian Defense Ministry didn’t respond to a request for comment. The move represents a remarkable setback for Russian President Vladimir Putin, whose military seizure of Crimea in 2014 marked...