Herbert Caldwell was born in Calcutta/Kolkata in India on 29 July 1905, the son of James Oswald Caldwell (a Sergeant in the Royal Welsh Fusiliers) and his wife Jane Caldwell.

Caldwell joined the Royal Navy at the age of sixteen as a Boy 2nd Class in Devonport. After time in HMS GANGES, HMS VIVID, HMS SOUTHAMPTON, HMS CHATHAM and HMS VALIANT, in December 1928 he became an officer and, after serving in HMS DRAGON in the West Indies, joined submarines as a Lieutenant in January 1932. After training, Caldwell served as Navigating Officer in HMS L69 (1932-1933) and HMS THAMES (1935); then as First Lieutenant in HMS L53 (1935) and HMS SEVERN (1936). After qualifying in 1938, he was appointed to command HMS H33 in December 1938.

Caldwell was promoted to Lieutenant Commander on 1 October 1939 and was appointed to command HMS TARPON in February 1940.  On 10 April 1940, TARPON was patrolling off Norway, when the German Q ship Schiff 40 was sighted and attacked. Schiff 40 counter-attacked with depth-charges and sank TARPON. There were no survivors.

Herbert Caldwell was the husband of Alice Violet Caldwell of Oxford. He is commemorated on the Portsmouth Naval War Memorial on Panel No. 36 Column No. 3.