This blog lists unit records for the United States Army from the start of the US participation in World War I through the 1930s. The bulk of the series listed focus on World War I, as wartime records were more likely then peacetime records to be retained permanently.  This is not a comprehensive list of all records of all US Army organizations, but instead focus on divisions, brigades, regiments, battalions, companies, trains, Air Service units, and medical units. These records are in the custody of the National Archives at College Park - Textual Reference Branch. For more information, contact them via email at archives2reference@nara.gov.

See Records Relating to Civil War Units and WWII Military Unit Records at the National Archives for other wars.

Divisions

• Records of Divisions, 1917 - 1920
• Divisional History Charts, 1918–1920
• Brief Histories of Divisions, 1918–1918
• 29th Division Station Lists, Histories, and Rosters, 1917–1919
• Records of Infantry Divisions, 1923–1940
• Inspection Reports of Armies, Divisions, and Corps, 1917–1919
• Daily Situation Reports of U.S. Armies, Army Corps, and Divisions, 1918–1919
• Summaries of Intelligence of U.S. Armies, Army Corps, and Divisions in France, 1918–1919
• Summaries of Intelligence, Reports, Bulletins, Press Reviews, and Other Issuances of U.S. Armies, Army Corps, Divisions, and Other Units of the American Expeditionary Forces, 1917–1919
• Journals of Operations, March 1, 1918–August 31, 1919
• Records Relating to the Operations of Armies, Corps, and Divisions, 1918–1919
• Correspondence Relating to Training Schedules and Programs for Armies, Corps, and Divisions, 1917–1919
• Reports of Divisions, Regiments, and Other Units, 1918–1919
• Index of Movements of Corps and Divisions, 1917–1919

Brigades

• Records of Infantry Brigade, 1917 - 1919
• Records of Infantry Brigades, 1923–1939
• Correspondence and Other Papers Relating to Officers, Infantry Organizations, and Maneuvers of the 4th Brigade at Fort Sam Houston, 1911–1927
• Railway Artillery Reserve (30th Artillery Brigade)
• Records of Artillery Brigades, 1917–1919
• Records of Field Artillery Brigades, 1917 - 1919
• Correspondence Relating to Field Artillery Brigades, 1918–1919
• Correspondence With First Army Artillery Brigades and Regiments, 1918–1919
• Correspondence and Reports Related to 2nd Provisional Brigade Fleet Landing Exercise Operations in Puerto Rico, 1937–1938
• Records of the 1st Cavalry Brigade, 1917–1919
• Records of Tank Brigades, 1918–1921
• American Forces in Germany (First Brigade)
• American Forces in Germany (Second Brigade)

Regiments

• Records of Cavalry Regiments, 1916–1937
• Special Orders of Cavalry Regiments, 1920–1941
• Records of [Coast Artillery] Regiments Numbered 1 through 75, 1916-1934
• Records of Coast Artillery Regiments, 1922–1939
• Records of Engineer Regiments and Battalions, 1912–1921
• Records of Engineer Regiments, 1919–1939
• Railway Engineer Regiments Records, 1917–1919
• Records Relating to the 10th and 20th Engineer Regiments, 1917–1918 (Forest Service)
• Records of Field Artillery Regiments Numbers 1 through 351, 1912–1930
• Returns and Rosters of Field Artillery Regiments, 1917–1921
• General Orders and Unit History Files of Various U.S. Artillery Regiments, 1934–1968
• Records of the 1st Through 338th and the 559th Infantry Regiment, 1916-1921
• Records of Infantry Regiments, 1922–1942
• Records of Pioneer Infantry Regiments, 1917 - 1919
• Records of Provisional Regiments, 1912–1936
• Issuances of Provisional Regiments Nos. 1-4 at Le Mans, 1918–1919
• Records of Quartermaster Regiments, 1923–1939
• Correspondence of the General Manager Relating to Railway Engineer Regiments, 1917–1919
• Railway Engineer Regiments Records, 1917–1919
• Stevedore Regiment Records, 1918–1919

Battalions

• Records of the 1st - 6th Anti-Aircraft Battalions, 1918–1918
• Records of Engineer Regiments and Battalions, 1912–1921
• Correspondence, Special Orders, and Other Records Relating to Topographical Engineer Companies and Battalions, 1917–1919
• Issuances of Provisional Battalions Nos. 103-281, 1919–1919
• Records of Provisional Ordnance Battalions, 1918–1919
• Records of Signal Depot Battalions, 1917–1919
• Records of Telegraph Battalions, ca. 1917–ca. 1920
• Records of Trench Mortar Artillery Batteries and Battalions, 1917–1919
• Records of Machine Gun Battalions, 1917–1920
• Records of the 122nd - 124th, 130th, and 134th Battalions, Military Police Corps
• Records of Provisional Guard and Fire Battalions, 1918–1919
• Records of the 304th - 355th Service (Labor) Battalions
• Records of the 401st-435th, 437th-439th, 441st-449th and 551st Reserve Service (Labor) Battalions
• Records of Field Signal Battalions, 1917–1922
• Records of Tank Battalions, 1918–1919
• Records of the 2nd, 17th, and 18th Tank Battalions, 1921–1931
• General Records Relating to the 7th Machine Gun Battalion of the First Brigade, 1917–1921
• Records of United States Guard Battalions, 1917–1919

Companies

• Correspondence, Special Orders, and Other Records Relating to Topographical Engineer Companies and Battalions, 1917–1919
• Records of Postal Express Companies A - L, 1918–1919
• Records of Casual Companies, 1918–1919
• Correspondence of Truck Companies A - F, 1918–1919: First Army Artillery Park
• Correspondence of the General Manager Relating to Transportation Companies, 1918–1919
• [Transportation Corps] Company Records, 1918–1919
• Records of the Transportation Corps Casual Companies at Camp de Grasse, 1918–1919
• Records of the Companies of the 1st Gas Regiment, 1918–1922
• Records of Military Police Companies, 1918–1919
• Military Police Companies Correspondence, 1918–1919
• Records of Butchery Companies, 1918–1919
• Records of the Garden Service Companies and the Garden Service Detachment at Is-Sur-Tille, 1918–1919
• Records of Laundry Companies, 1918–1919
• Records of Provisional Laundry Companies and Provisional Laundry Units, 1918–1919
• Records of Refrigerating Plant Companies, 1918–1919
• Records of Supply Companies, 1917–1919
• Records of Wagon Companies, 1918–1919
• Records of Tank Corps Casual Companies B and C, 1918–1919
• Records of Training and Replacement Companies, 1918–1919
• Records of Motor Transport Corps Administrative Companies Nos. 1-7, 9, and 11, 1918–1919
• Records of Tank Repair and Salvage Companies, 1918–1919
• Records of Motorcycle Companies, 1917–1919
• Records of Companies of the Provisional Guard Battalion, 1919–1921
• Records of Cement Mill Companies, 1918–1919
• Correspondence Relating to Cement Mill Companies, 1918–1919
• Records of Administrative Labor Companies, 1918–1919
• Records of the 1st and 2nd Censor and Press Companies, 1918–1919
• Records of Cook Companies, 1918–1919
• Records of the Depot Service and Labor Companies, 1918–1919
• Records of the Guard and Provisional Guard Companies, 1918–1920
• Records of Prisoner of War Escort Companies, 1918–1919
• Records of Rents, Requisitions, and Claims Companies, 1918–1919

Trains

• Records of Ammunition Trains, 1917–1920
• Records of Engineer Trains, 1917–1919
• Records of Engineer Pontoon Trains, 1918–1919
• Records of Pack Trains, 1917–1919
• Records of Supply Trains, 1917–1919
• Records of Motor Supply Trains, 1917–1919
• Records of Water Tank Trains, 1918–1919

Air Service / Air Corps Squadrons, Regiments, Companies and Wings

• Records of the 1st through 1111th Aero Squadrons, 1917 - 1919
• Correspondence Relating to Aero Squadrons, 1919 - 1930 (documenting 1917 - 1930) 
• Card File of Movements of Aero Squadrons, ca. 1917 - ca. 1919
• Correspondence of Balloon Wing Companies D, E, and F, 1918–1919
• Records of the 1st - 4th Mechanics Regiments, 1917–1919
• Records of the 1st - 9th Casual Companies, 1918–1919
• Records of the 11th, 14th, 23rd, 72nd, and 96th Bombardment Squadrons, 1918–1939
• Records of the 13th, 18th, and 27th Reconnaissance Squadrons, 1936–1941
• Records of the 1st, 2nd, 48th, 51st, and 61st School Squadrons, 1923–1939
• Records of the 1st, 4th, 12th, 15th, 16th, 21st, 44th, 50th, 82nd, and, 99th Observation Squadrons, 1918–1940
• Records of the 58th, 59th, and 69th Service Squadrons, 1922–1936
• Records of the 5th, 8th, 9th, and 12th Air Base Squadrons, 1935–1939
• Records of the 1st through 9th Recruit Squadrons, 1918–1919
• Records of the 808th and 816th Depot Aero Squadrons, 1918–1922
• Records of the 1st, 2nd, 3rd, and 18th Wings, 1934–1941

Medical, Ambulance, Hospital, and Infirmaries

• Records of Medical Regiments, 1918–1924
• Records of Units, 1917–1919 (U.S. Army Ambulance Service with the French Army)
• Records of Medical Units and Offices of Infantry Divisions, 1917–1919
• Reports Relating to Hospital Trains, 1918–1919
• Records of Hospital Trains, 1917–1919
• Records of Mobile Surgical Units, 1918–1919
• Records of Infirmaries, 1917–1919
• Records of Infirmaries, Field Hospitals, and Sanitary Trains, 1919–1923
• Records of Medical Detachments and Infirmaries of the Air Service, 1917–1919
• Records of Infirmaries of Cavalry Brigades and Regiments, 1917–1919
• Records of Infirmaries of Engineering Regiments and Other Units, 1917–1919.
• Records of Infirmaries of Units of the Quartermaster Corps, 1917–1919
• Records of Infirmaries of Units of the Signal Corps, 1917–1919
• Records of Infirmaries of Ammunition, Supply, Water Tank, and Troop Transport Trains, 1917–1919
• Records of Infirmaries of the 1st Through 320th Train Headquarters and Military Police Companies, 1917–1919
• Transportation Corps Infirmary Units Records, 1917–1919
• Records of Medical Units of the Motor Transport Corps, 1917–1919
• Records of Infirmaries of Headquarters and Battalions of the U.S. Guards, 1917–1919
• Historical Records of Motor Ambulance Companies, 1917–1919
• Historical Records of Evacuation Ambulance Companies, 1917–1919
• Historical Records of Nondivisional Field Hospital Companies, 1917–1919

General and Other

• Historical Files, 1918–1948
• Card File of Military Engagements of American Organizations, 1918–1918 aka Lists of Military Engagements of American Organizations ("Battle Credit File")
• Tables of Organization, 1921–1921
• Special Operations Reports, 1917–1919
• Records of the 1st, 2nd, 5th - 7th, and 12th - 24th Grand Divisions: American Expeditionary Forces. Services of Supply. Transportation Corps.