Jennings was born in Brooklyn, New York, attended the Colorado School of Mines, and studied engineering and literature at Columbia University.

[2] He had his first experience of seafaring at age 19 as a hand aboard a tramp steamer in the Black Sea and eastern Mediterranean.

[citation needed] As of October 1940, aged 33, he was living in Wayland, Massachusetts, and was self-employed.

[3] In World War II, he served as a lieutenant in the US Navy and was head of the Naval Aviation History Unit.

Banners Against the Wind (1954) was a biographical novel about the pioneering doctor Samuel Gridley Howe.