John Armstrong, Jr. (November 25, 1758 – April 1, 1843) was an American soldier and statesman who was a delegate to the Continental Congress, U.S. Senator from New York, and Secretary of War.
John Jr. was the son of Dr. John Armstrong and Rebecca (Lyon) Armstrong and was born in Carlisle, Pennsylvania in 1758. After early education in Carlisle he studied at the College of New Jersey (now Princeton University). He broke off his studies in Princeton in 1775 to return to Pennsylvania and join the fight in the Revolutionary War.

Revolutionary War
While in camp with Gates at Newburgh, New York, Armstrong became involved in the Newburgh Conspiracy. He is generally acknowledged as the author of the two anonymous letters directed at the officers in the camp. The first, titled "An Address to the Officers" (dated March 10, 1783), called for a meeting to discuss back pay and other grievances with the Congress and form a plan of action. After General Washington ordered the meeting canceled and called for a milder meeting on March 15th, a second address appeared that claimed that this showed that Washington supported their actions.
Washington successfully defused this protest without a mutiny. While some of Armstrong's later correspondence acknowledged his role, there was never any official action that connected him with the anonymous letters.

Later life

Skeen, Carl E.; John Armstrong, Jr., 1758–1843: A Biography; 1982, Syracuse Univ Press; ISBN 0-8156-2242-2.