Andy Stapp, who expressed his opposition to the Vietnam War by joining the Army and proceeding to do a very unmilitary thing — form a union among soldiers that demanded, among other things, the right to elect officers and reject what they viewed as illegal orders — died on Sept. 3 in Manhattan. He was 70.

His wife, Deirdre Griswold, said the cause was complications of a lung infection.

At its peak in the early 1970s, the union that Mr. Stapp formed, the American Servicemen’s Union, claimed to have tens of thousands of members. It issued membership cards, published a newspaper and helped form chapters at military bases, on ships and in Vietnam.

Although the Army never came close to recognizing the union formally, it certainly recognized it as a problem. Mr. Stapp brought colorful idealism to his counterintuitive cause, and the Army did what it could to silence him.

In 1967, while stationed at Fort Sill in Lawton, Okla., Mr. Stapp twice faced court-martial. The first time was for refusing an order to open his footlocker, which served as his unit’s library of leftist literature. (Officers broke it open with an ax.) He was convicted and served 45 days of hard labor. The second was based on charges that he had left his barracks when he was forbidden to do so. He was acquitted in late 1967.