This series includes drafts and retained copies of the letters that du Pont sent to his 1,500 correspondents. The letters are arranged chronologically, and each is identified by a Winterthur number.

Instead of keeping a private journal as many officers did in order to document their experiences at sea, du Pont addressed a series of more than 400 letters to his wife, which he assumed would serve as a semi-official record of his various overseas cruises and assignments. There are another 950 letters to Sophie Madeleine du Pont included in the collection, but these are, for the most part, personal in nature.

This series also contains du Pont's official letter books for the cruises of the Congress and the Cyane (October 1845-October 1848); the cruise of the Minnesota (May 1857-May 1859); the commission in charge of the Japanese embassy (1860); and the command of the South Atlantic Blockading Squadron (September 1861-July 1863).

Du Pont's involvement in the naval reform movement is documented in letters to Stockton, George S. Blake, Percival Drayton, Matthew C. Perry, Benjamin Isherwood, Matthew Fontaine Maury, and Alexander Slidell MacKenzie. This correspondence describes many of the problems that the Naval Efficiency Board attempted to solve. From du Pont's perspective, the most important concerns were nepotism, political favoritism, and inadequate officer education. The correspondence indicates that he was somewhat ambivalent about the need to recognize the contributions of technically trained staff officers. He did recommend that the curriculum of the Naval Academy include rigorous training in science and mathematics.

Du Pont's correspondence during the Civil War years is extremely voluminous. There are more than 1,000 letters and official dispatches addressed to Secretary Gideon Welles and his assistant, Gustavus Fox. These describe the operations of the South Atlantic Blockading Squadron and the successful assault on Port Royal. The files also document the establishment of a naval base on South Carolina's Sea Islands as well as du Pont's efforts to come to terms with the social implications of the Port Royal Experiment, which raised many of the questions about the place of the Black man in American society that would surface again during Reconstruction.

The letters from 1862 and 1863 clearly show that du Pont had serious reservations about the reliability of monitors but that he rarely expressed his thoughts to Welles or Fox. du Pont's efforts to defend himself after he was relieved from his command are described in more than 190 letters to Henry Winter Davis. This series also includes copies of letters, letter books, and journal-letters that were transcribed at the direction of Sophie du Pont or Colonel Henry A. du Pont.