Divisions of the United States Army This list of United States Army divisions is divided into three eras : 1911 – 1917 , 1917 – 1941 , and 1941 – present . These eras represent the major evolutions of army division structure ( there have been several minor changes during these times ) . The 1911 – 1917 era lists divisions raised during the Army ' s first attempts at modernizing the division , prior to the authorization of permanent divisions , and the 1917 – 1941 era lists the first permanent divisions , prior to advent of specialized ( armored , airborne , etc . ) divisions . The 1941 – present era lists all of the divisions organized , raised , or authorized since then . As much as possible , divisions are only listed in the eras in which they were first created . Some divisions , such as the 1st Cavalry Division , are listed in multiple eras , as their organizations were drastically changed from one era to the next . Many divisions overlap the years listed in the era categories , mainly due to the slow pace in which they were deactivated , inactivated , or otherwise disbanded . It should also be noted that several divisions have existed under multiple designations , such as the 10th Mountain Division ( 10th Light Division ( Alpine ) , 10th Infantry Division ) . Additionally , several divisions with the same numerical designations were completely separate and unrelated divisions ( there have been two 5th Divisions , for instance ) . History . Divisions in the United States Army have existed since the American Revolution when , on 22 July 1775 , George Washington organized three divisions in Boston , Massachusetts . Early American divisions , up until the American Civil War , were primarily temporary organizations , with the basis of the United States Army being brigade s and regiments . During the Civil War , the war in which formed the first large true armies in United States history , divisions were formed primarily to support Army corps , and were usually numbered as 1st , 2nd , and 3rd Division of the pertaining corps . The concept of the permanent United States Army division was formulated and put to the test following the turn of the 20th century . In 1916 , the permanent division would finally be authorized by Congress , resulting in a dramatic change in the Army ' s force structure . For the first time , the division was the base element of the United States Army and remained as such until the Global War on Terrorism , when the Army switched its emphasis to brigade and regimental combat team s . Since the authorizations of permanent divisions , the United States Army has raised 128 separate divisions with unique lineages . Designations . Prior to 1941 , only cavalry divisions were specifically designated ; infantry divisions were simply designated by " Division " . Following the advent of the armored division , infantry divisions became officially designated by " Infantry Division " ( with the 25th Infantry Division being the first constituted by the adjutant general as such ) . All of the 1917 – 1941 ( non - cavalry ) divisions , with the exceptions of the 10th through 20th and 101st Divisions , would be redesignated as Infantry Divisions at some point in the 1941 – present era . Other than the aforementioned Armored , Cavalry , and Infantry , the only official Army division designations are Air Assault ( one test division ) , Airborne , Light ( three test divisions in World War II ) , Motorized ( briefly authorized from 1942 to 1943 ) , and Mountain . For lineage purposes , the 101st Airborne Division maintains its designation as an airborne division , though it is currently organized as an air assault division . Divisions listed with an additional identifier in parentheses ( " alpine " or " test " , for example ) existed only with that identifier . Divisions that have held multiple additional identifiers , such as the 1st Cavalry ( " airmobile " , " heavy " ) and the 9th Infantry ( " light " , " motorized " ) , are left unidentified , regardless of their current additional identifier . An unspecified division today refers to a United States Army Reserve training division . Divisions of the United States Army ( 1911 to 1917 ) . National Defense Act of 1916 . The National Defense Act of 1916 provided that the " Army of the United States " would consist of the Regular Army , the Volunteer Army , the Officers ' Reserve Corps , the Enlisted Reserve Corps , the National Guard in the service of the United States , and such other land forces as were or might be authorized by Congress . The president was to determine both the number and type of National Guard units that each state would maintain . Both the Regular Army and the National Guard were to be organized , insofar as practicable , into permanent brigades and divisions . Divisions of the United States Army ( 1917 to 1941 ) . Cavalry divisions . In 1940 , the National Guard voluntarily withdrew their allotment of the 21st through 24th Cavalry Divisions , partially in response to the Army ' s decision that the National Guard did not need four Cavalry Divisions and the Army ' s unwillingness to allot the National Guard armored divisions . The 61st through 66th Cavalry Divisions existed primarily as officer billets with enlisted cadre ; they were dropped from the activation rolls and disbanded in 1942 . Infantry divisions . Various elements of the 4th through 9th Divisions remained on active duty until those divisions ' full activation prior to World War II . The 76th through 91st and 94th through 104th Divisions existed primarily as officer billets with enlisted cadre ; they were not completely reactivated until America ' s entry into World War II . The infantry brigades , field artillery brigades , and several other of the subordinate units of the Panama Canal , Hawaiian , and Philippine Divisions were numbered accordingly with what should have been the 10th , 11th , and 12th Divisions . Divisions of the United States Army ( 1941 to present ) . Infantry divisions . The 105th and 107th Infantry Divisions were intended to be negro divisions of the Army of the United States ; however , due to a shortage of available manpower , their activations were canceled in 1942 . Reserve training divisions . In an attempt to maintain its divisions , the Army Reserve transformed several of its combat divisions into training divisions ; these divisions were still designated as infantry divisions until authorized as " divisions ( training ) " by the adjutant general in 1959 . Divisions planned but never actually formed during the Second World War . At the time of the Japanese attacks on Pearl Harbor , Wake Island , and the Philippines , the United States Army was composed of 37 divisions , including the Philippine Division . Initially , necessary mobilization was estimated to be as high as 350 divisions , but the Army ultimately settled on a 100 - division plan . This relatively low number ( compared to the high estimates ) was partially due to the army ' s policy of assigning many combat units , particularly artillery and tank destroyer units , directly to corps and higher - level commands . These non - divisional units numbered approximately 1 . 5 million soldiers , enough personnel to man roughly 100 more divisions . The strategic philosophy was that such units could be assigned to divisions on as - needed bases , and would allow divisions to remain as mobile and flexible as possible . By the end of 1943 , U . S . Army strength stood at more than 70 divisions . Allied gains in 1942 and 1943 resulted in a further contraction of U . S . mobilization , and the last wartime division , the 65th Infantry Division , was activated on 16 August 1943 . In all , 91 divisions served in the U . S . Army in World War II . When the decision was made to halt the increase in divisions , 12 more divisions were still on the rolls , but would not be organized , though several of these would be organized following the war . They were the 15th Airborne Division , the 18th , 21st and 22nd Armored Divisions , the 19th Armored Division , which was in fact activated following the war , the 61st , 62nd , 67th , 68th , 72nd , 73rd , and 74th Infantry Divisions , and the 105th and 107th Infantry Divisions , which were intended to be Negro formations . Unique among the 14 unorganized divisions , the 15th Airborne Division was not only a victim of the decision to set the size of the Army at 89 divisions ( the 2nd Cavalry Division had been deactivated during the war and the Philippine Division was destroyed as a result of the Japanese victory in the Philippines ) , but also because it had become evident that the Army Air Forces lacked enough transport aircraft to support a sixth airborne division . The 13th Airborne Division never saw combat for this very reason . The 105th and 107th Infantry Divisions were to join the 92nd and 93rd Infantry Divisions as Negro divisions . A shortage of manpower resulted in the activation of the 105th and 107th being cancelled in 1942 .