During 1839 he served with the West Indies Squadron and the receiving ship in Baltimore, before being assigned to the Pacific Squadron in 1843. He became Fleet Surgeon with the Pacific Squadron in 1844 and, upon completion of his tour in 1846, was about to return to the United States when relations between that country and Mexico became decidedly strained. The commander of the Navy's Pacific Squadron, Commodore John D. Sloat, consequently entrusted certain dispatches to Wood to carry back to the United States with him. Wood volunteered to travel through Mexico and report upon conditions there. Accompanied by the American consul from Mazatlán, Mexico, the former fleet surgeon commenced his journey across Mexico.