However, 45 minutes
after Pleasants lit the fuse
there was no explosion. Pleasants attempted to check the problem
himself, but two of his men entered the
mine ahead of him. They determined that
there was a loss in fuse continuity at a splice location. The splice was fixed, and the fuse was successfully
lit, resulting in a massive eruption that shocked men
on both sides of the lines.
While all sources agree that the explosion was
significant and the resulting crater was large, the
actual dimensions of the crater appear uncertain.
In his book In the Trenches at Petersburg: Field Fortifications & Confederate Defeat (Chapel Hill, North
Carolina: University of North Carolina Press, 2009), Earl J.
Hess claims it was approximately 125 ft long and 50 ft wide.
Corrigan, on the other hand, suggests it was 200 ft long and
50 ft wide. The National Park Service provides an approximation of 170 ft for the length and 60 to 80 ft for the width.
Most sources appear to agree that the crater had a depth of
30 ft. The elongated shape of the crater derived from the fact
that the gunpowder had been placed in a number of separate magazines rather than at a single location. With the
1,000 lb of powder used per mine branch magazine and an
LLR of approximately 22 ft, the resulting crater should have
been approximately 88 ft wide. The difference between the
reported crater width and the estimate from Duane’s equation is probably a reflection of the physical influence of the
heavily fortified salient.
While Pleasants and his men accomplished
an unprecedented feat of military engineering,
the ensuing assault went poorly. Burnside had
prepared the assaulting units by rehearsing the
assault for at least a week. Two days prior to the
assault Meade switched the attacking units and
changed the maneuver plan. While Burnside’s
units were well rehearsed, they were largely un-
tested in battle. Meade was concerned about using
untested troops to lead the charge. By drawing
lots from Burnside’s hat, Brigadier General James
Ledlie, who commanded Burnside’s 1st Division
and was regarded by his peers (and subsequently
by historians) as Burnside’s worst subordinate,
became responsible for leading the attack. Once
the Union soldiers overcame the initial shock of
the crater explosion, they charged forward with
support from 110
Union guns and 54
mortars. As the Union
soldiers rushed the Confed-
erate lines across the no-man’s-
land and entered the crater, the
men began digging to form defen-
sive positions. They also attempted
to dig out Confederate soldiers bur-
ied by the blast. The crater was soon
full of Union troops holding their position
instead of charging up and out of the crater. They
became easy targets for the Confederate guns aimed
down into the depression. Union officers would
eventually stir their men to press forward, but lit-
tle progress was made, especially once Confederate
reinforcements responded. The day ended in a failed breach
and a defeat for the Union.
AT ITS WORST the Battle of the Crater represents the tre- mendous bloodshed of the Civil War, but at its best it stands as a great achievement of military engineering. Sadly, within a span of just seven hours, 4,000 Union and 1,500 Confederate soldiers were killed, wounded, or captured. If the Union forces had successfully capitalized on their breach and seized Petersburg, it is likely that
the war would have ended much earlier. Instead, the fight for
Petersburg dragged on for nearly a full year.
Although postbreach operations failed, the engineering behind the breach was a success. Pleasants and his men
expertly exploited the soil conditions available,
made the most of the supplies that were available,
and constructed a mine that many of their superiors thought would be physically impossible. CE
Second Lieutenant Colin Hennessy, M.ASCE, is serving in the infantry branch of the U.S. Army. Brock E.
Barry, Ph.D., P.E., M.ASCE, is an associate professor in
the civil and mechanical engineering department at the
United States Military Academy at West Point, where
he is responsible for geotechnical engineering and engineering mechanics courses. The authors wish to acknowledge
the technical and professional guidance provided by Paul
F. Mlakar, Ph.D., P.E., Dist.M.ASCE, a senior scientist
at the U.S. Army Corps of Engineers’ Engineer Research
and Development Center. Currently on sabbatical leave
from the center, Mlakar holds the Class of 1953 Distinguished Chair in Engineering at West Point.
aT iTs worsT The baTTle of The craTer represenTs The
Tremendous bloodshed of The civil war, buT aT iTs besT iT
sTands as a greaT achievemenT of miliTary engineering.