In 1909 Nicaraguan President José Santos Zelaya of the Liberal Party faced opposition from the Conservative Party, led by governor Juan José Estrada of Bluefields who received support from the U.S. government. The United States had limited military presence in Nicaragua, having only one patrolling U.S. Navy ship off the coast of Bluefields, in order to protect the lives and interests of American citizens who lived there. The Conservative Party sought to overthrow Zelaya which led to Estrada's rebellion in December 1909. Two Americans, Leonard Groce and Lee Roy Cannon, were captured and indicted for allegedly joining the rebellion and the laying of mines. Zelaya ordered the execution of the two Americans, which severed U.S. relations. The forces of Chamorro and Nicaraguan General Juan Estrada, each leading conservative revolts against Zelaya's government, had captured three small towns on the border with Costa Rica and were fomenting open rebellion in the capital of Managua. U.S. Naval warships that had been waiting off Mexico and Costa Rica moved into position. The protected cruisers USS Des Moines , USS Tacoma , and collier USS Hannibal  lay in the harbor at Bluefields, Nicaragua, on the Atlantic coast with USS Prairie  en route for Colón, Panama, with 700 Marines. On December 12, 1909, Albany with 280 bluejackets and the gunboat USS Yorktown  with 155, arrived at Corinto, Nicaragua, to join the gunboat USS Vicksburg  with her crew of 155 to protect American citizens and property on the Pacific coast of Nicaragua.
Question: How many crewman combined were on the USS Yorktown and Vicksburg?
Answer: 310