brigadier general on August 29, 1916. World War I With the April 1917 American entry into World War I, Lejeune assumed command of the newly constructed Marine Barracks, Quantico, Virginia; however, his overseas service was inevitable, and in June 1918, he arrived at Brest, France. He was promoted to major general on July 1, 1918. Upon reporting to General John Joseph "Blackjack" Pershing, Commander-in-chief (CinC) of the American Expeditionary Forces (AEF) on the Western Front, he was assigned to succeed Charles R. Boardman in command of the 164th Brigade of the 32nd Division but later assumed command of the 4th Marine Brigade, part of the 2nd Division, immediately following the attack of the division in the Battle of Soissons, with Earl Hancock Ellis serving as the brigade's adjutant. On July 28, 1918, Major General Lejeune assumed command of the U.S. Army's 2nd Division. He was the second Marine officer to hold an Army divisional command, Marine Brigadier General Charles A. Doyen having previously commanded the division for two weeks. Lejeune commanded the 2nd Division during the victorious action at the battle of St. Mihiel in September. The operation was a success, and Lejeune sent an order of congratulations to the men of his command: Lejeune emphasized tightly coordinated action that emphasized extensive rehearsal and disciplined artillery gunnery. This discipline enabled infantry elements to follow closely behind barrages that would otherwise be far too risky. This "leaning on the artillery" meant that the enemy faced direct assault while still reverting from the shock of a bombardment. Lejeune stated his philosophy as "The key to combat effectiveness is unity – an esprit that characterizes itself in complete, irrevocable, mutual trust. Now my infantry trusts my artillery and engineers, and my artillery and engineers know this so they will go through hell itself before they let down the infantry. My infantry believe that with such support they are invincible-and they are." Marshal Pétain praised Lejeune as "a military genius who could and did do what the other commander said couldn't be done." During the war, he was recognized by the French government as a strategist and leader, as evidenced by the Legion of Honor, and the Croix de guerre bestowed upon him by France. The C-in-C of the AEF, General Pershing, awarded Lejeune the U.S. Army's Distinguished Service Medal. The citation for his Army DSM reads: The U.S. Navy's Distinguished Service Medal was