Close up view of the bow of the USS Constitution. The ship is constructed of white and longleaf pine, white oak, and, most importantly, southern live oak. The latter is particularly dense, heavy, and difficult to work, but very strong. Because her hull was built 53 cm (21 in) thick in an era when 47 cm (18 in) was common, she was able to withstand cannonades, thus earning the nickname of "Old Ironsides." The copper sheathing along the keel prevents the attachment of shipworms.