On May 27, the 48th Massachusetts took part in the first assault on Port Hudson. 200 volunteers were called on from their division for a storming party to lead the division's charge and lay down fascines to allow passage over ditches and trenches. Such a storming party was known as a "Forlorn Hope." The 48th Massachusetts supplied half the number of volunteers needed for this detail. During the assault, however, the extremely rugged ground and tangle of felled trees proved too difficult and neither the storming party nor the main assault made sufficient progress. The 48th Massachusetts reached the foot of the Confederate earthworks and enduring constant firing from the enemy. The regiment lost six killed and 41 wounded during this assault, including Lt. Col. James O'Brien. O'Brien was shot and killed as he led the "Forlorn Hope" and exposed himself to severe fire largely in an effort to redeem himself and the regiment for his error in allowing the enemy to outflank them at Plains Store.