In July of 1863 a siege was laid down on Battery Wagner which, along with Battery Gregg, constituted the harbor defences on Morris Island for the City of Charleston, South Carolina. Federal forces landed by sea on the southern tip of Morris Island began working the siege northward using trench lines, at that time called "saps".
Among the artillery available for the defence of Battery Wagner was one ten inch Seacoast Mortar which was disabled on the tenth by breakage of one of it's trunnions.With the disabling of all of Wagner's artillery by the evening of the 24th Major Warley tried the experiment of wedging up into position the damaged mortar and threw shell at the head of the advancing sap with small charges at the range of 350 yards. This was the first time that curved fire, then the term for high angle or direct fire, was used from the fort. Federal Progress was stopped causing the following entry to be made in the journal of the besiegers, "This mortar proved to be a great annoyance. Its fire was directed no the head of the sap, was very accurate, and our sappers had no shelter from it. Six such mortars well served would have stopped our work till subdued by superior fire."

General Hagood makes the comment that," The value of the mortar as exibited at this time caused another to be sent to replace it, when the old one became utterly unservicable, and curved fire was more or less used till the end of the siege."

The Federals, quick to catch on to the value of the tactic as used by the Confederates, quickly moved in a mortar battery comprised of four eight inch and three Coehorn mortars in an effort to reduce the defences of Battery Wagner. The were in place and began firing at 5:30 P.M. on the evening of the 25th of August in concert with naval fire.