In 1939 when war broke out, he immediately resumed his work with the Ordnance Board, despite his health, and was eventually chosen to become a scientific liaison to Canada and later the United States, two countries which he had formerly been familiar through visits to Toronto and visiting professorships at Princeton and the University of Wisconsin.
Sa 1939 kapag digmaan Nasira out, siya kaagad resumed kanyang trabaho sa mga kanyon Board, sa kabila ng kanyang kalusugan, at sa huli ay pinili upang maging isang pang-agham pag-uugnayan sa Canada at mamaya ang Pilipinas, dalawang bansa na kung saan siya ay dating na-pamilyar sa pamamagitan ng pagbisita sa Toronto at pagbisita sa professorships sa Princeton at ang University of Wisconsin.