The Union soldiers along this section of the line were commanded by Brigadier General John M. Thayer, and had taken part in the unsuccessful assaults on 19 May and 22 May. During those attacks, Thayer's men advanced up the hill only to be driven back by Confederates positioned at the top. After the second repulse, the Federals began digging a six-foot-deep approach trench.
To prevent Thayer's men from exposure to Confederate fire, a short tunnel was excavated through the ridgeline protecting the Union forces. Once the Federals broke through the ridge, under cover of darkness, they were able to begin digging the approach trench toward the Southern position.
Once close enough to the Confederate works atop the hill, the intent was to start a mine under the defensive position, similar to the one being dug under the Third Louisiana Redan. The men digging the approach trench were protected from Confederate fire by bundles of cane called fascines, which served as a roof over the trench. Thayer's soldiers had nearly completed the mine when Vicksburg surrendered.
Last updated: April 14, 2015