It was decided to sink the collier Merrimac at a narrow point in the channel, where, lying full length, she would completely prevent egress.

It was a delicate task and one of extraordinary danger.

It was characteristic of the spirit of the fleet that, as Admiral Chadwick says, practically all the men were volunteers.
The honor of the command was given to Lieutenant Richmond Pearson Hobson, Assistant Naval Constructor, who had been in charge of the preparations.

With a crew of six men he entered the harbor mouth on the night of the 3d of June.

A shell disabled the steering gear of the Merrimac, and the ship sank too far within the harbor to block the entrance entirely.