Johnston's attack on Washington, D.C., during the battle of Antietam in Maryland on September 17, 1862.
Chamberlain was born on September 19, 1828, in Otsego County, New York. He was the tenth child of Gideon Talbot Chamberlain and his wife, Susan Talbot Chamberlain. His father was a farmer who died when he was 14 years old.
Two years later, when Joshua was 16 years old, his mother married John Trowbridge. They eventually had seven children together: Susan (1825-1875), George (1827-1894), John (1829-1877), Solomon (1830-1911), Benjamin (1831-1909), Mary (1833-1909), and Joseph (1836-1913).
During his childhood, Joshua worked hard to help his family make ends meet by farming and fencing their property. He also performed chores for neighbors to earn money for his mother and siblings.
Joshua entered military service at age 21 in July 1846 after graduating from West Chester Academy in Pennsylvania with honors in mathematics and Latin.
He enlisted for two years in Company H of the 2nd New York Artillery Regiment under Captain Lewis Collins.
On June 20, 1847, Chamberlain joined Company F of the 6th U.S. Infantry at Fort Hamilton in Brooklyn, New York, as an ensign with the rank of second lieutenant. He participated in campaigns against hostile Indians along the Oregon Trail to California and Mexico before the outbreak of the Mexican War on April 25, 1846.
He achieved the rank of first lieutenant by July 1, 1847 after participating in several battles against hostile tribes along the Santa Fe Trail to New Mexico Territory including Apache Pass near Gila Bend on March 29–30, 1847; The Battle of Apache Pass near Gila Bend on April 22–23, 1847; The Battle of San Luis Rey on May 12–13, 1846; The Battle of Churubusco on August 8–9, 1847; The Battle of Molino del Rey near Mexico City on September 13