Searching for letters, journals, and other personal and public documents referencing the life and military service of the three Clark brothers from Sangerville, Maine:

James Clark: Initially a first lieutenant in Company E of the Eighteenth Maine Infantry, he later became adjutant of the First Maine Heavy Artillery, and died of wounds on July 24, 1864.

Frank Clark: Initially a private in Company E of the First Maine Heavy Artillery, he rose to become a first lieutenant and mustered out of the army in 1866.

Whiting S. Clark: Initially captain of Company E of the Eighteenth Maine Infantry, he later became major of the First Maine Heavy Artillery, and left the regiment with a disability discharge in late 1865. He died in Des Moines, Iowa, on April 26, 1891.

Any and all help appreciated.