Career
Jennings specialized in the collecting of United States stamps and postal history, especially cancellations of stamps on cover. Jennings helped to provided leadership for the hobby. He encouraged stamp collecting by juniors, and served as mentor to collectors both young and old.
His knowledge of philately was extensive, and he was assigned by the American Philatelic Society to serve on juries of their stamp shows.
Because of his enthusiasm and strong ties to Florida, Jennings was a major force on the Florida Philatelic Exhibition (FLOREX) show committee of the Florida Federation of Stamp Clubs.