Ellis played major roles in the planning of the St. Mihiel (Champagne) (12–16 September 1918) and Meuse-Argonne (Champagne) Offensives (September 29 to October 10, 1918) including the attack on and capture of Blanc Mont Ridge, and in the Meuse-Argonne Offensive from October 31 to November 11, 1918. After Lejeune succeeded to command of the 2nd Division, Ellis's reputation as a strategist and planner led his brigade commander, Brigadier General Wendell Cushing Neville to recommended Ellis for an accelerated promotion to colonel. Ellis did not receive the promotion, but was awarded both the Navy Distinguished Service Medal and Navy Cross, which he received on November 11, 1920. In addition, France awarded him the Croix de guerre and Légion d'honneur (Grade of Chevalier).