[1][5] He served as a private in Colonel Jeremiah Moulton's Third Massachusetts Regiment, where he fought in King George's War (1744–48).

Recent sources suggest he fought in the French and Indian War (1754–63) at the age of 64, once again assisting in the capture of the Fortress of Louisbourg, and later in a military expedition against Chief Pontiac in 1763.

"[8] On April 19, 1775, British forces were returning to Boston from the Battles of Lexington and Concord, the opening engagements of the war.

Whittemore loaded his musket and ambushed the British grenadiers of the 47th Regiment of Foot from behind a nearby stone wall, killing one soldier.

[2][9] A monument stands in the corner plot (611 Mass Ave.) called Whittemore Park at the northeast corner of Massachusetts Avenue and Mystic Street in Arlington, Massachusetts; it reads (inaccurately as to age both at the time and 18 years later[3]): Near this spot, Samuel Whittemore, then 80 years old, killed three British soldiers, April 19, 1775.