A picture-book history illustrates the beginning of a new era in naval warfare. The age of wooden warships had come to an end. The Confederacy captured the shipyards of Portsmouth, Virginia, resurrected the Merrimack, and turned it into an ironclad fighting ship, intending to destroy Union ships in Norfolk and steam up the Potomac River to bomb Washington, D.C. Northern spies knew the plans, and an arms race began. “All the navies of the world were suddenly out-of-date.” Union leaders hired inventor John Ericsson to create a new fighting machine. In 100 days, the Monitor was designed and created, towed to Hampton Roads, Virginia, and led into one of the greatest naval battles of all time. On March 9, 1862, with thousands of people watching from the shore, the two ships fought to a draw, never to meet again. Confederate forces later burned the Merrimack, or Virginia to avoid having it captured by Union forces, and the Monitor sank in a storm. O’Brien’s clear and lively writing, dramatic watercolor and gouache illustrations, maps, and handsome, large-format design combine to make an appealing volume. An afterword explains how marine archaeologists found the Monitor off of Cape Hatteras in 1973, and the U.S. government has made the site of the wreck a national marine sanctuary. A sure-fire winner for young Civil War buffs. (Nonfiction. 6-10)