James Owen Mack Jr., whose career with Hercules Aerospace spanned four decades, died at age 70, on May 15, 1991, in Salt Lake City.

Under Mr. Mack's management, the Hercules rocket chamber-winding plant at Clearfield became the most modern and best-equipped in the country, a company official said in 1980.After graduating from the University of Missouri at the age of 20 in 1941, he began a career at Hercules' corporate headquarters in Wilmington, Del. He transferred to the Sunflower Army Ammunition Plant in Kansas, and then to the Allegheny Ballistics Laboratory in Maryland, where he helped develop the submarine-based Polaris missile. In 1959, he began working as manufacturing manager at the Bacchus Works and was based in Salt Lake City.

After assignments at a Hercules ammonia plant in Pennsylvania and back in Kansas, he was named manager of the fiberglass and graphite rocket motor chamber plant in Clearfield. In 1980, Mr. Mack was appointed Hercules' vice president and general manager at the Radford, Va., ammunition plant. He retired in Salt Lake City four years later.

Services will be held at 2 p.m. Saturday, May 18, at First Presbyterian Church, C Street and South Temple. A private burial service will be held for family members at Wasatch Lawn Memorial Park.