british prime minister lord palmerston sent a fleet of naval warships to the western atlantic in preparation for a surprise attack on new york city. they intended to use the world's largest ship, the ss great eastern as a troop transport. they saw a strike against new york would be a strike against the u.s. center of commerce. but in the spring of 1862, the british learned of the union ironclad warship, the uss monitor. this cancelled any invasion plans. while the british navy had ironclad warships, they required deep water to navigate. the monitor and northern ships like her could destroy british ships should they try to blockade northern ports. russia was also concerned the british and/or french might step in. during the summer of 1862, a coalition of nations considered stepping in to mediate the war. these included britain, france, prussia, austria and russia. but in the fall of 1863, tsar alexander ii of russia sent his navy to protect the united states from any invasion by great britain and france. their baltic fleet began arriving in new york harbor on september 24, 1863. the russian far east fleet was sent to san francisco.