To bring the Union Army close against the Confederate defense line,
construction of protected approaches was begun. As the siege progressed,
"saps" or "approach trenches," deep enough to conceal troops, zigzagged
their way toward the works protecting Vicksburg. Ten major approaches
were carried forward by pick and shovel details, each with a network of
parallels, bomb proofs, and artillery emplacements. Over 60,000 feet of
trenches and 89 artillery positions, mounting 220 guns, were completed.
In the siege of Vicksburg "Spades were trumps."