At a part of the Union line that was only from the Confederate line, the 48th Pennsylvania regiment was dug in. They were below the top of a ridge and part of their lines could not be seen by Confederates, blocked by the terrain. The 48th Pennsylvania regiment was made up of anthracite coal miners. Their commander heard his men remark, "We could blow that damned fort out of existence if we could run a mine shaft under it!" He passed the idea up to Burnside who agreed to the idea and digging started on June 25. Confederates on the ridge began to hear the sounds of picks and shovels under them. They dug several listening shafts. But when the digging sounds stopped on 23 July, they quit looking and dismissed any danger from mining. By the afternoon of July 28 the explosives were ready. Burnside's Fourth Division, including nine regiments of African American troops were trained to bypass the crater the explosion would cause and attack immediately after the explosion. These were fresh troops and their morale was high. At the last minute, Burnside's plan was changed by his commander General Meade to send in white troops. Meade said he did not want to be responsible for the "massacre" of colored troops.