On June 6, 1918, at the Battle of Belleau Wood, he was severely wounded in action. For his conspicuous service on that date, GySgt Janson was awarded both the Army and Navy Medals of Honor. The French Médaille militaire, with the accompanying Croix de guerre with Palm, the Italian Croce al Merito di Guerra, the Montenegrin Medal for Military Bravery and the Portuguese Medalha da Cruz de Guerra Third Class were also awarded to him for the same act of bravery.