Served on board the U.S.S. Oneida in the engagement at Mobile Bay, 5 August 1864. Severely wounded, Preston remained at his gun throughout the engagement which resulted in the capture of the rebel ram Tennessee and the damaging of Fort Morgan, carrying on until obliged to go to the surgeon to whom he reported himself as "only slightly injured." He then assisted in taking care of the wounded below and wanted to be allowed to return to his battle station on deck. Upon close examination it was found that he was wounded quite severely in both eyes.