Dan Abnett 
Monitor versus the Merrimac [PDF ebook] 

In this historic clash in March 1862, the Union Monitor, called by many a "cheese box on a raft, " exchanged cannon shot after cannon shot with the Confederate Merrimac, comically referred to as a "floating barn roof." Although an indecisive victory for either side, the spectacular event, witnessed by hundreds of people on nearby boats and shorelines, forever changed the way naval warfare was to be fought.