During the 16th and 17th centuries, the Cossacks conducted military campaigns against the Crimean Khanate and the Ottoman Empire, using sailboats and rowboats. The Don Cossacks called them "strugs" ("струг"). These boats were capable of transporting up to 80 men. The Cossack flotillas numbered 80 to 100 boats. The centralized Russian state had been fighting for its own access to the Baltic Sea, Black Sea and Sea of Azov since the 17th century. By the end of that century, the Russians had accumulated some valuable experience in using riverboats together with land forces.