Retired Navy Adm. John Mylin Will, 81, an expert in submarine warfare who later commanded what is now the Military Sealift Command, died Friday at Walter Reed Army Medical Center. He had cancer.

Adm. Will, who maintained homes in Deerfield Valley, Va., and New York City, joined American Expert Lines after retiring from the Navy in 1959. He served as president of the company from 1959 to 1965 and as chairman of the board from 1960 until 1971. He recently retired as president and chairman of the Arthur Tickle Engineering Works Inc., a marine engineering company.

A native of Perth Amboy, N.J. Adm. Will graduated from the U.S. Naval Academy at Annapolis in 1923 and later earned a master's degree at Pennsylvania State University.

He joined the submarine service and commanded submarine divisions in the Pacific during World War II. His postwar assignments included the Bureau of Personnel in the Navy department, where he was director of training, and command of the cruiser Columbus.

In 1949, he was named commander of the Military Sea Transportation Service for the Atlantic. Subsequently, he was director of personnel policy in the Office of the Secretary of Defense. In 1956, he was appointed to the command of the entire MSTS, now the Military Sealift Command. He held this post until his retirement.

Adm. Will's military decorations included three Legions of Merit. Because of these awards, he was promoted from vice admiral to full admiral on his retirement.

His wife, the former Louise Ley, died in 1969.

Survivors include a son, Navy Capt. John M. Jr., of Fort Foote, Md.; two brothers retired Navy Capt. Prentis K., of Cape Elizabeth, Maine, and Otto W. Jr., of Metuchen, N.J. and four grandchildren.