As a loyal supporter of the Royalist cause, like many Italian officers Messe soon found himself re-employed, when after the Italian armistice in September 1943, he was made Chief of Staff of the "Italian Co-Belligerent Army" (Esercito Cobelligerante Italiano), consisting of those units loyal to King Victor Emmanuel, many of which were reconstituted from Italian POWs and armed by the Allies. He served in this post with distinction until the war's end and then retired from the military in 1947 after 46 years of distinguished service.