After his father is killed fighting for the Union, thirteen-year-old Tom Carroll takes a job at a Brooklyn ironworks to support his family. He quickly learns that they are building an ironclad "unsinkable" ship to be called the Monitor to finally sink the Confederates' "unsinkable" ship, the Merrimac.

This is a brilliantly written description of a major sea battle through the eyes of a teenaged boy who both helped build the Monitor and fought on it.