Whittemore began his railroad career in 1913 as a clerk in the
Boston and Maine Railroad's
Concord, New Hampshire car shop. He left the railroad in 1917 to join the
United States Army. He rose to the rank of lieutenant and returned to the B&M after his discharge in 1919. However, after a couple of months he left the railroad to become a municipal accountant for the New Hampshire Tax Commission. In 1922, he became the general manager of Fellows & Sons Lumber Co. In this role, Whittemore supervised the company's mills, log drives, and industrial plants. From 1925 to 1929, he was a member of the New Hampshire Tax Commission. He helped organize
Boston-Maine Airways and served as its vice president until federal regulations barred railroads from the aviation business. On August 31, 1948, Whittemore was elected president of the New York, New Haven and Hartford Railroad. He resigned from the Federal Reserve Bank of Boston on October 4, 1948. He resigned a president of the New Haven on December 21, 1949, in order join the Brown Company. He took over as Brown's president on January 1, 1950, and on October 20, 1952, took on the additional role as chairman of the board of directors. Under Whittemore's leadership, the papermaker began producing a number of new products, including
chloroform and
shoe inserts. In 1955, he served as a special advisor and observer for President
Dwight D. Eisenhower at the
Geneva Round of the
General Agreement on Tariffs and Trade multilateral trade negotiations. Whittemore was also a director of
Amoskeag Company,
New England Telephone and Telegraph Company, National Life Insurance Co.,
Peerless Insurance,
H. P. Hood and Sons,
State Street Bank and Trust Company, and
Boston and Albany Railroad. He was also a trustee of the
Brookings Institution and
New Hampshire Historical Society and chairman of the
Crotched Mountain Rehabilitation Center. ==Later life==