 McClellan had also placed hopes on a simultaneous naval approach to Richmond via the James River . That approach failed following the Union Navy 's defeat at the Battle of Drewry 's Bluff , about 7 miles ( 11 km ) downstream from the Confederate capital , on May 15 . Basing artillery on a strategic bluff high above a bend in the river , and sinking boats to create an impassable series of obstacles in the river itself , the Confederates effectively blocked this potential approach to Richmond . 
