Book "Chancellorsville and Gettysburg" by Major General Abner Doubleday. Charles Scribner's Sons, NY 1882.

Page 170. "The 20th Maine made a grand final charge, and drove the rebels from the valley between the Round Tops, capturing a large number of prisoners. Not a moment too soon, for Chamberlain (Col. Joshua Chamberlain) had lost a third of his command and was entirely out of ammunition."