Elihu Root was a former US Secretary of War and Secretary of State who served as a member of the American delegation to the 1921 Washington Naval Conference. During the conference Root was a representative on the sub-conference on the limitation of armament and proposed a number of resolutions on commerce raiding and submarine warfare.

These were subject to prolonged discussions by the conference as a whole. The French delegates were less than keen on several of Root's proposals, which sought to ban outright or at least severely limit the use of submarines and torpedoes in war, since the use of such weapons appeared to offer a way by which the French armed forces could challenge British naval supremacy (possibly a remnant of pre-war Jeune Ecole theory, although I'm not knowledgeable enough about French naval strategy to state that with any degree of confidence). This brought the French into conflict with the British (and to a lesser extent the US) delegations, which strongly supported efforts to restrict submarine warfare. It is therefore not surprising that you should find Root and his proposals referenced in contemporary French diplomatic cables.

Reports and proceedings of the conference are a matter of public record, and several versions of these have been digitised.

• The report of the American delegation, including Root himself, is available through JSTOR.

• Root's proposals are reported in full in Appendix 9 of the report of the Canadian delegation to the conference.

• The British government report on the final treaty, including the submarine and piracy regulations which originated in Root's proposals, are also available for download from the FCO.

Edit: added reference to FCO report

Thank you very much ! I’ll look into it !