Seth Ledyard Phelps was of the Old Navy and the New. As a midshipman and junior officer he served under sail off West Africa, in the War with Mexico, and in the Mediterranean and Caribbean. As a senior office in the river squadrons of the Civil War he saw combat at its closest.

Phelps, a native of Chardon, Ohio, was a prolific and observant correspondent. His private letters, to his wife, his father, and to political patrons and other naval officers, are among the most compelling and descriptive extant.

The heart of Ironclad Captain are these letters, which Jay...