author
b. 1892
A Royal Naval Reserve officer who turned wartime experience into vivid nonfiction, he is best known for writing about life inside a submarine during and just after the First World War. His work brings the routines, risks, and close quarters of undersea service to life in a direct, readable way.

by Mark Herbert Joseph Bennett
Born in 1892, Mark Herbert Joseph Bennett is listed by Project Gutenberg as the author of Under the Periscope. Contemporary prefatory material to that book says he served throughout the war as an officer in a British submarine and was also an officer in His Majesty’s Mercantile Marine.
That background gives Under the Periscope its appeal. Rather than reading like distant history, it feels grounded in first-hand knowledge of submarine work, the men who served in it, and the unusual demands of naval life below the surface.
Firm biographical details beyond his birth year and service background are hard to confirm from the sources I found, so his public record appears to rest mainly on this surviving book and its connection to wartime submarine service.