Battle of Saint - Mihiel The Battle of Saint - Mihiel was a World War I battle fought between September 12 – 15 , 1918 , involving the American Expeditionary Force and 48 , 000 French troops under the command of General John J . Pershing of the United States against German positions . The United States Army Air Service ( which later became the United States Air Force ) played a significant role in this action . This battle marked the first use of the terms ' D - Day ' and ' H - Hour ' by the Americans . The attack at the St . Mihiel Salient was part of a plan by Pershing in which he hoped that the United States would break through the German lines and capture the fortified city of Metz . It was one of the first U . S . solo offensives in World War I and the attack caught the Germans in the process of retreating . This meant that their artillery were out of place and the American attack proved more successful than expected . Their strong blow increased their stature in the eyes of the French and British forces , but again demonstrated the critical role of artillery during World War I and the difficulty of supplying the massive World War I armies while they were on the move . The U . S . attack faltered as artillery and food supplies were left behind on the muddy roads . The attack on Metz was not realized , as the Germans refortified their positions and the Americans then turned their efforts to the Meuse - Argonne offensive . Background : Saint - Mihiel salient . Saint - Mihiel is a town in the Meuse department in north - eastern France . Since the end of the 1870 Franco - Prussian War the town was no longer considered important strategically and military installations were not developed . This changed early in World War I with the town inside the battlefront . In 1914 the German command wished to take the Verdun fortifications which formed a strong point in the French lines . A first attempt , at Bois - le - Pretre ( " Priesterwald " in German ) , failed despite violent fighting . During two more attempts ( Battle of Flirey ) German troops took Saint - Mihiel and the fort at Camp des Romains , but they were ultimately stopped at the Fort de Troyon to the south of Verdun . During the course of the war the battlefront did not change much in this area . Saint - Mihiel formed a salient inside the French lines , blocking communications between Nancy and Verdun . The area near St . Mihiel would know much fighting : But despite French attacks the German forces were able to retain this strategic location until the last months of the war . Prelude . General John Pershing thought that a successful Allied attack in the region of St . Mihiel , Metz , and Verdun would have a significant effect on the German army . General Pershing was also aware that the area ' s terrain setting first dictated that the restricted rail and road communications into Verdun ( restrictions that had been imposed by the German attack during the Battle of Flirey ) be cleared , and that a continuation of the attack to capture the German railroad center at Metz would be devastating to the Germans . After these goals were accomplished , the Americans could launch offensives into Germany proper . Weather reports . The weather corps of Corps I Operation Order stated : " Visibility : Heavy driving wind and rain during parts of day and night . Roads : Very muddy . " This would pose a challenge to the Americans when the order to advance was given . In some parts of the road , the men were almost knee - deep in mud and water . After five days of rain , the ground was nearly impassible to both the American tanks and infantry . Many of the tanks were wrecked with water leakage into the engine , while others would get stuck in mud flows . Some of the infantrymen developed early stages of trench foot , even before the trenches were dug . German defensive positions . Prior to the American operation , the Germans installed many in - depth series of trenches , wire obstacles , and machine - gun nests . The battlefields ' terrain included the nearby premises of three villages : Vigneulles , Thiaucourt , and Hannonville - sous - les - Cotes . Their capture would accelerate the envelopment of the German divisions near St . Mihiel . The American forces planned to breach the trenches and then advance along the enemy ' s logistical road network . The Germans knew many details about the Allied offensive campaign coming against them . One Swiss newspaper had published the date , time , and duration of the preparatory barrage . However , the German Army stationed in the area of St . Mihiel lacked sufficient manpower , firepower and effective leadership to launch a counter - attack of its own against the Allies . Thus , the Germans decided to pull out of the St . Mihiel Salient and consolidate their forces near the Hindenburg Line . The Allied forces discovered the information on a written order to the German Group Armies von Gallwitz . Allied tank support . Although the AEF was new to the French theater of war , they trained hard for several months in preparation of fighting against the German armies . The use by the British of tanks at the Battle of Cambrai in 1917 impressed General Pershing so much that he ordered the creation of a tank force to support the AEF ' s infantry . As a result , by September 1918 , Colonel George S . Patton Jr . had finished training two tank battalions - 144 French - built Renault FT light tanks organized as the 344th and 345th battalions of the United States Tank Corps - at Langres , France for an upcoming offensive at the St . Mihiel salient . In addition to the AEF tanks , the attack was supported by a further 275 French tanks ( 216 FTs and 59 Schneider CA1 medium tanks ) of the French 1st Assault Artillery Brigade ; a total of 419 tanks . Battle . The St . Mihiel offensive began on 12 September with a threefold assault on the salient . The main attack was made against the south face by two American corps . On the right was the I Corps ( from right to left the 82d , 90th , 5th , and 2d Divisions in line with the 78th in reserve ) covering a front from Pont - à - Mousson on the Moselle westward to Limey ; on the left , the IV Corps ( from right to left the 89th , 42d , and 1st Divisions in line with the 3rd in reserve ) extending along a front from Limey westward to Marvoisin . A secondary thrust was carried out against the west face along the heights of the Meuse , from Mouilly north to Haudimont , by the V Corps ( from right to left the 26th Division , the French 15th Colonial Division , and the 8th Brigade , 4th Division in line with the rest of the 4th in reserve ) . A holding attack against the apex , to keep the enemy in the salient , was made by the French II Colonial Corps ( from right to left the French 39th Colonial Division , the French 26th Division , and the French 2d Cavalry Division in line ) . In First Army reserve were the American 35th , 80th , and 91st Divisions . The Allies also mobilized 1 , 481 aircraft to provide air superiority and close air support over the front . Defending the salient was German " Army Detachment C " , consisting of eight divisions and a brigade in the line and about two divisions in reserve . The Germans , now desperately short of manpower , had begun a step - by - step withdrawal from the salient only the day before the offensive began . The attack went so well on 12 September that Pershing ordered a speedup in the offensive . By the morning of 13 September the 1st Division , advancing from the east , joined hands with the 26th Division , moving in from the west , and before evening all objectives in the salient had been captured . At this point Pershing halted further advances so that American units could be withdrawn for the coming offensive in the Meuse - Argonne sector . Order of Battle , First Army , 12 September 1918 . First Army ( United States ) - Gen . John J Pershing List of American Balloon Squadrons Aftermath . General Pershing ' s operational planning of St . Mihiel separated the salient into several sectors . Each Corps had an assigned sector , by boundaries , that it could operate within . The American V Corps location was at the northwestern vertice s , the II French Colonial Corps at the southern apex , and the American IV and I Corps at the south - eastern vertices of the salient . Furthermore , General Pershing ' s intent was obvious ; to envelope the salient by using the main enveloping thrusts of the attack against the weak vertices . The remaining forces would then advance on a broad front toward the direction of Metz . This pincer action , by the IV and V Corps , was to drive the attack into the salient and to link the friendly forces at the French village of Vigneulles , while the II French Colonial Corps kept the remaining Germans tied down . One reason for the American forces ' success at St . Mihiel was General Pershing ' s thoroughly detailed operations order . Pershing ' s operation included detailed plans for penetrating the Germans ' trenches , using a combined arms approach to warfare . His plan had tanks supporting the advancing infantry , with two tank companies interspersed into a depth of at least three lines , and a third tank company in reserve . The result of the detailed planning was an almost unopposed assault into the salient . The American I Corps reached its first day ' s objective before noon , and the second day ' s objective by late afternoon of the second . Another reason for the American success was the audacity of the small unit commanders on the battlefield . Unlike other officers that commanded their soldiers from the rear , Colonel Patton and his subordinates would lead their men from the front lines . They believed that a commander ' s personal control of the situation would help ease the chaos of the battlefield .