 He first worked on whaling ships out of the Pacific Northwest, then sailed the Pacific as a merchant mariner.Halstead joined the U.S. Navy from his home state of New York and served over two years on the , suppressing the slave trade off the coast of Africa in the 1850s.Following the onset of the Civil War, he helped enforce the Union blockade at the mouth of the Mississippi River and was present at the capture of New Orleans in 1862.