The biggest favour they could do the Union was to desert

From Warriors: Portraits from the Battlefield by Max Hastings. Page 46.

Professor Chamberlain becomes Lieutenant-Colonel Chamberlain, second-in-command of the 20th Maine.

The men of the 20th Maine were volunteers aged between eighteen and forty-five, enlisted for three years, and now commanded by Colonel Adelbert Ames, an ambitious twenty-six-year-old not long out of West Point, who had earned promotion by his courage during the Union defeat at First Bull Run, the earliest major battle of the war, where he won the Congressional Medal of Honor. Arrived at the encampment of his new command, instead of a sentry's salute Ames received an outstretched hand and the greeting, "How d'ye do, Colonel." He took one horrified look at the shambling crowd of recruits for whom he had become responsible, and said: "This is a hell of a regiment." In one of his gloomier moments, he urged the Maine men that the biggest favour they could do the Union was to desert. They had no more notion of soldiering than Professor Chamberlain, and precious little time in which to acquire one.