, a pontoon bridge was laid at a point known as Chaffin's Bluff, and this was soon thereafter used to transfer reinforcements to the line between the James
and Appomattox rivers
, and to Petersburg
At the same time, one company of engineer troops was detachedd with a pontoon train and sent to Petersburg
, where a bridge was needed to facilitate crossing the Appomattox River
at that point.
Of the eleven companies of engineer troops which remained north of the James
during General Grant
's first operations against Petersburg
, one company was in charge of the pontoon bridge at Chaffin's Bluff and ten served as infantry on what was known as the Deep Bottom
As soon as it became known to General Beauregard
that an attempt was being made to undermine a salient point on his line, he made use of the company of engineer troops then at Petersburg
, in an effort to protect the threatened point by countermining.
Two pits were sunk in the trenches, from the bottom of which drifts or tunnels were extended some distance beyond the entrenchments, and a circumvallating gallery was in progress, which, if it had been completed in time, might have discovered the exact location of the underground approach of the foe: although it was subsequently ascertained that while the drift by which the Federals
reached a point under the Confederate
lines was about half-way between the two Confederate workings, it was at a somewhat lower level.
However, the Confederate
works were incomplete when, on July 30, 1864, the Federal
mine was exploded.
The most lasting effect of this demonstration by General Grant
was to produce a feeling of impending danger at every salient point of the Confederate
line of defense; and General Lee
ordered eight more companies of engineer troops from north of the James
, and made large details from the infantry to swell their numbers, in order to expedite the work of countermining, which, from that time on, was pushed energetically, until ample protection was afforded at all points