about 3:30
The main sap was run some 500 feet , until it was under a fort on Cemetery Hill . Wings were constructed to the right and left of the sap or tunnel , so that about four tons of powder were placed under the fort , tamped with sand bags and wood . The intention was to explode the mine , and at the moment of the explosion to open with all the artillery in this front on the enemy 's lines , and to rapidly move a storming column through the crater and carry the high ground in rear , which , if in our possession , would command the city and the enemy 's works . At about 3:30 on the morning of the 30th of July the fuse was lighted , but no explosion followed . Many attempts were made before the powder ignited . The suspense was great . Silent was quietly waiting to see the result .