John P. Carroll Jr., a retired tax partner at Davis Polk & Wardwell credited with inventing the foreign currency swap, died at his summer home in Massachusetts on July 12. He was 84.

During World War II, Mr. Carroll was stationed in China with the U.S. Marine Corps. He enrolled at Harvard Law School after the war, graduating in 1949. Following another military stint during the Korean War, he joined the chief counsel’s office of the Internal Revenue Service in 1953.