Damian Shiels's Green and Blue explores Irish American service in the United States military by analyzing the written correspondence of ordinary rank-and-file soldiers drawn from across the Union's armed forces. Using a vast and largely untapped collection of letters penned by Irish American combatants to their families during the war, Shiels explains how these enlisted men navigated their duties from multiple perspectives, including how they adapted to and experienced military life, how they engaged with their faith, and how they interacted with the home front. Green and Blue offers the most detailed and intimate picture yet of Irish Americans' service in the United States military during the Civil War.