In the Full Sap

Men of the sapping details rest and work in a wide trench under a crest of gabions — the full sap, the siege's slowest and most dangerous digging, with the camps spread out on the sand behind.

The full sap began at two in the morning on 19 August 1863, when the tide had gone down enough to make it possible, with a sapping brigade of ten men of the New York engineers under Captain Walker; officers relieved one another over it in roughly six-hour tours, and progress ran slow but constant through soil that hit water two feet down. Haas & Peale's plate is the portrait of that arithmetic.