Every man in the investing line became an army engineer day and night.
The soldiers worked at digging narrow, zigzag approaches to the rebel
works. Entrenchments, rifle pits, and dirt caves were made in every
conceivable direction. When entrenchments were safe and finished,
still others, yet farther in advance were made, as if by magic, in a
single night. Other zigzag underground saps and mines were made for
explosion under forts. Every day the regiments foot by foot, yard by
yard, approached nearer the strongly armed rebel works. The soldiers
got so they bored like gophers and beavers, with a spade in one hand
and a gun in the other.
With an almost limitless ammunition supply, Federal sharpshooters and
artillerymen kept up a relentless fire, giving the Confederates little
opportunity to pick off the work parties which continued digging
operations during the day. Pemberton's ammunition supply dwindled each
day. Considering the possible duration of the siege until an effective
relief army might be assembled, the Confederate commander considered it
"a matter of vital importance that every charge of ammunition on hand
should be hoarded with the most jealous care." He therefore issued
strict orders that both rifle and cannon should be fired only when
absolutely necessary. This prevented the Confederates from keeping up
the steady, harassing fire needed to hold in check the Union siege
activities.
Trench life for Grant's soldiers was not so rigorous or dangerous as for
the Vicksburg defenders. Food supplies were ample, although lack of pure
water was a problem for both armies and resulted in considerable
disease. The burning sun and frequent rains made life miserable for both
"Yank" and "Reb." Particularly as a result of the low ammunition stores
of the Vicksburg army, Union losses during the siege, after the assaults
of May 19 and 22, were comparatively light.
After the unsuccessful assault of May 22, only two attempts were made to
break through the Confederate defenses, neither of which succeeded.
Sherman, holding the Union right opposite the strong Fort Hill position,
determined to reduce the fort with naval aid, and on May 27 the gunboat
_Cincinnati_, protected by logs and bales of hay, moved into position
and engaged the several batteries of that sector. Subjected to a deadly
plunging fire which "went entirely through our protection--hay, wood,
and iron," the _Cincinnati_ went down with her colors nailed to the
stump of a mast.
The other attempt to pierce the defense line was by exploding a mine
under the Third Louisiana Redan. Logan's approach trench had reached the
fort walls and from here a shaft was sunk under the fort and a powder
charge prepared for its demolition. The Confederate garrison, hearing
the miners' picks at work beneath the fort, began countermines in a grim
race for survival. On June 25, as the entire Union line opened fire to
prevent shifting of reinforcements, a charge of 2,200 pounds of powder
was exploded beneath the Third Louisiana Redan, creating a large crater
into which elements of the 23rd Indiana and 45th Illinois raced from the
approach trench. Anticipating this result, General Forney had prepared a
second line of works in the rear of the fort where survivors of the
blast and supporting regiments met the Union attack and drove it back.
Still other mines were also being prepared by Union engineers at the
time of the surrender.