For 18 months in the early days of the American Civil War, no man had more direct responsibility for the health and well-being of millions of Union soldiers than Dr. Jonathan Letterman. As Medical Director for the great Army of the Potomac, he was tasked with providing guidance and directives for the setup of hospitals, treatment of wounds and illness, diet for men in the field, and assignments of other medical personnel. Here is Letterman's own words is the summary of that enormous task, written just after the close of war. He saw it all and met the major military and political men of his time, serving initially under General George Brinton McClellan. Most fascinating are his assessments of what was needed to keep the army healthy and able to fight. He also includes anecdotes of his time in the field and around battles.