ten o’clock
This force was gradually transferred to the flag-ship , and the other two vessels sailed out of the bay just before darkness came on , as if in chase of some ship they had sighted -- a ruse well calculated to lull the Spaniards into security . The men intended for the service then took their places in fourteen boats that lay hidden behind the flag-ship . All were dressed in white , with a blue band on the left arm , in order that they might distinguish each other in the dark . At ten o'clock the boats pushed off in two directions , commanded respectively by Captain Crosby and Captain Guise , while the admiral led the way in his launch . It was just twelve o'clock when the boats arrived at a small opening in the boom . The oars had been muffled , and so perfectly had silence been observed , that the admiral 's launch ran against a guard-boat lying at the entrance , without its approach having been observed by the Spaniards . There was a hasty challenge by the startled officer in command , to which the admiral himself replied by threatening the occupants of the boat with instant death if they gave the slightest alarm .