One of these periods away was when he went to head the Ballistics Research Laboratory at the Aberdeen Proving Ground, Maryland in 1942-45 during the Second World War. His joint treatise Exterior Ballistics written during this period, and published in 1953, was considered the leading work on ballistics at the time.
Isa sa mga panahon na ang layo kapag siya ay napunta sa ulo ang Ballistics Research Laboratory sa Aberdeen Proving Ground, Maryland sa 1942-45 habang ang Second World War. Magkalakip ang kanyang treatise panlabas Ballistics nakasulat na panahon na ito, at nai-publish sa 1953, ay itinuturing ang nangungunang trabaho sa ballistics sa oras.