Thomas Weldon was born at 3 Bryanston Mansions, York Street, Marylebone, London, in 1896.

After an education at Tonbridge School, he won a scholarship to read Literae humaniores at Magdalen College, Oxford, which he postponed to become an officer in the Royal Field Artillery in 1915.

He spent World War I in France and Belgium, rising to acting captain, being wounded and winning the Military Cross and bar.

His final duties there involved justifying Harris's controversial bombing strategy to politicians and the public.

[1] In a review in the London Review of Books of a newly published work by Niall Ferguson, R. W. Johnson said that it amounted to a tutorial: "The idea is to teach the young to think and argue, and the real past masters at it (Harry Weldon was always held up as an example to me) were those who first argued undergraduates out of their received opinions, then turned around after a time and argued them out of their new-found radicalism, leaving them mystified as to what they believed and suspended in a free-floating state of cleverness."