After his brother is wounded at Fredericksburg in 1862, Whitman goes to Washington to take care of him and stays on to visit the wounded in the Washington hospitals.
One of the first sights that greets him is a pile of amputated legs and arms, for the .58 caliber Minie balls or bullets, fired at slow velocity, resulted in shattered bones and gaping wounds and infections.
Whitman visits the wounded every day for several years, until his health breaks down.  He writes letters, reads to the men, brings them goodies--tobacco, which he doesn’t use himself, fruit, brandy--and lifts their spirits.
Whitman’s experiences in New York with helping hurt stage and wagon drivers was helpful.
During this time, he met Peter Doyle, to whom he became close for a period of several  years.