Infantry timelines · Infantry numbers 1–200

21st Infantry Regiment

A century of division assignments

1916–2026 · Regimental service, battle groups, battalions and deployments.

21st Infantry Regiment unit graphic
21st Infantry Regiment
First division shown16th Division (World War I)29 Jul 1918
Separate battalion histories5 documented elementsDated lineages and service notes below
Page cutoff8 September 2026Last-documented status is explicitly marked

One regiment, separate assignments

The common row follows the regiment. After its reorganization, battle groups and battalions could hold different assignments at the same time. A deployment or temporary attachment does not by itself change the assigned division. The common row closes on 5 Jun 1958; later service belongs to the separate element rows. Battalion rows follow headquarters lineages, often descended from lettered companies, rather than assuming that the old regimental battalions continued unchanged.

The Hawaiian Division was reorganized as the 24th Infantry Division in 1941. Formal division assignments are distinguished from brigade attachments in Vietnam.

Division patches

Hawaiian Division24th Infantry Division25th Infantry Division63d Infantry Division23d Infantry Division (Americal)11th Airborne Division

Representative division patches. Patterns could change over time; an image does not imply that the exact version was worn throughout every period. Divisions without a verified asset remain identified by name.

The dated record

Division timeline

Battalion overview →

Deployments, operations and credited campaign service appear inside assignment cards. Award years establish credited service, not exact tour dates. Some service notes identify only company-sized elements. This is a sourced selection, not a complete movement log.

Assignment ends are exclusive: the next period starts on that date. *Striped final bars mean last documented, with later status unverified through the page cutoff. Unknown intervals are not treated as inactive.

  1. 1 Jan 1916 – 29 Jul 1918

    21st Infantry Regiment

    Assignment not established

    The available record does not establish a precise assignment throughout this interval. No division is inferred.

    Source

  2. 29 Jul 1918 – 8 Mar 1919

    21st Infantry Regiment

    16th Division (World War I)

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

  3. 8 Mar 1919 – 22 Oct 1921

    21st Infantry Regiment

    No assigned division

    The cited record establishes service outside an assigned division. Higher headquarters and temporary operational attachments could still direct the unit.

    Source

  4. 22 Oct 1921 – 26 Aug 1941

    21st Infantry Regiment

    Hawaiian Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

  5. 26 Aug 1941 – 5 Jun 1958

    21st Infantry Regiment

    24th Infantry Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

    Deployments & overseas operations

    1. 1944-1945

      New Guinea, Leyte and Southern Philippines

      21st Infantry Regiment · Campaign service

      Campaign participation is recorded in the Army lineage. The year label summarizes campaign service, not an exact overseas tour.

      Source

    2. 1950-1953

      Korea

      21st Infantry Regiment · Campaign service

      Campaign participation is recorded in the Army lineage. The year label summarizes campaign service, not an exact overseas tour.

      Source
  6. 5 Jun 1958 – 15 Apr 1970

    1st Battle Group / Battalion lineage

    24th Infantry Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

  7. 15 Apr 1970 – 5 Jun 1972

    1st Battle Group / Battalion lineage

    Inactive

    The unit or its headquarters lineage was inactive. This status does not imply that every inherited honor or divisional affiliation was erased.

    Source

  8. 5 Jun 1972 – 16 Oct 2005

    1st Battle Group / Battalion lineage

    25th Infantry Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

  9. 16 Oct 2005 – page cutoff*

    1st Battle Group / Battalion lineage

    Last documented: 25th Infantry Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage. The source establishes this last recorded status, not uninterrupted service through 2026. The striped bar extends to the page cutoff to keep the later research gap visible.

    Source

    Deployments & overseas operations

    1. 2007-2009

      Baghdad, Iraq

      1st Battle Group / Battalion lineage · Credited overseas service

      The Army lineage lists a unit decoration for service in these years. These are credited service years, not exact deployment and return dates.

      Source

    2. 2010-2011

      Iraq

      1st Battle Group / Battalion lineage · Credited overseas service

      The Army lineage lists a unit decoration for service in these years. These are credited service years, not exact deployment and return dates.

      Source
  10. 5 Jun 1958 – 1 May 1959

    3d Battle Group / Battalion lineage

    Inactive

    The unit or its headquarters lineage was inactive. This status does not imply that every inherited honor or divisional affiliation was erased.

    Source

  11. 1 May 1959 – 1 Apr 1963

    3d Battle Group / Battalion lineage

    63d Infantry Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

  12. 1 Apr 1963 – 15 Sep 1965

    3d Battle Group / Battalion lineage

    Inactive

    The unit or its headquarters lineage was inactive. This status does not imply that every inherited honor or divisional affiliation was erased.

    Source

  13. 15 Sep 1965 – 15 Feb 1969

    3d Battle Group / Battalion lineage

    196th Infantry Brigade · Separate

    This headquarters is not a division. Temporary attachments in the service entries below are distinct from the formal assignment.

    Source

  14. 15 Feb 1969 – 1 Nov 1971

    3d Battle Group / Battalion lineage

    23d Infantry Division (Americal)

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

    Deployments & overseas operations

    1. 1969-1971

      Vietnam

      3d Battle Group / Battalion lineage · Credited overseas service

      The Army lineage lists a unit decoration for service in these years. These are credited service years, not exact deployment and return dates. More than one assignment falls in the opening year; this year-level service marker does not establish the assignment on a particular deployment day. The labeled service overlaps an assignment change and is listed only once; consult the following assignment cards as well.

      Source
  15. 1 Nov 1971 – 23 Aug 1972

    3d Battle Group / Battalion lineage

    196th Infantry Brigade · Separate

    This headquarters is not a division. Temporary attachments in the service entries below are distinct from the formal assignment.

    Source

  16. 23 Aug 1972 – 16 Jan 1986

    3d Battle Group / Battalion lineage

    Inactive

    The unit or its headquarters lineage was inactive. This status does not imply that every inherited honor or divisional affiliation was erased.

    Source

  17. 16 Jan 1986 – 15 Jul 1995

    3d Battle Group / Battalion lineage

    25th Infantry Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

  18. 15 Jul 1995 – 16 Mar 2002

    3d Battle Group / Battalion lineage

    Inactive

    The unit or its headquarters lineage was inactive. This status does not imply that every inherited honor or divisional affiliation was erased.

    Source

  19. 16 Mar 2002 – 1 Jun 2006

    3d Battle Group / Battalion lineage

    25th Infantry Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

    Deployments & overseas operations

    1. 2005

      Nineveh Province, Iraq

      3d Battle Group / Battalion lineage · Credited overseas service

      The Army lineage lists a unit decoration for service in these years. These are credited service years, not exact deployment and return dates.

      Source
  20. 1 Jun 2006 – 16 Dec 2006

    3d Battle Group / Battalion lineage

    Inactive

    The unit or its headquarters lineage was inactive. This status does not imply that every inherited honor or divisional affiliation was erased.

    Source

  21. 16 Dec 2006 – 6 Jun 2022

    3d Battle Group / Battalion lineage

    25th Infantry Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage.

    Source

    Deployments & overseas operations

    1. 2008-2009

      Iraq

      3d Battle Group / Battalion lineage · Credited overseas service

      The Army lineage lists a unit decoration for service in these years. These are credited service years, not exact deployment and return dates.

      Source
  22. 6 Jun 2022 – page cutoff*

    3d Battle Group / Battalion lineage

    Last documented: 11th Airborne Division

    Division names are normalized across historical redesignations. This entry follows the cited unit lineage. The source establishes this last recorded status, not uninterrupted service through 2026. The striped bar extends to the page cutoff to keep the later research gap visible.

    Source

Service note · dates incomplete

2d Battalion · Hawaii and Germany

The regimental history describes the 2d Battle Group with the 25th Infantry Division, later the 2d Battalion with the 24th Infantry Division, and inactivation in April 1970.

Source

Service note · dates incomplete

4th Battalion · Vietnam and Panama

Deployed to Vietnam in 1968 with the 196th Infantry Brigade; assigned to the Americal Division in February 1969. Later participated in Operation Just Cause with the 7th Infantry Division in 1989.

Source

Service note · dates incomplete

5th Battalion · Panama

Participated in Operation Just Cause in 1989 with the 7th Infantry Division, including an air assault at Coclecito.

Source

Sources and scope

Army Center of Military History lineage certificates provide the dated backbone. Regimental associations and secondary histories supplement individual operations and battalions. Where the evidence stops, the page says so. A page cutoff is not a claim that every unit directory was current on that date.

Earlier battalions are covered by common regimental service; separately dated lineages and substantiated later battalions receive their own rows or notes. A unit graphic alone is not evidence of a battalion assignment. Reserve, training and inactive organizations are distinguished from active combat units.

  1. U.S. Army Center of Military History: 21st Infantry Regiment
  2. U.S. Army Center of Military History: 1st Battalion 21st Infantry Regiment
  3. U.S. Army Center of Military History: 3d Battalion 21st Infantry Regiment
  4. Military Review: Arctic Angels and the 2022 reflagging
  5. Army Historical Foundation: 21st Infantry Regiment
  6. 21st Infantry Regiment history (Wikipedia; secondary)

Patch artwork

Unmodified artwork from Wikimedia Commons; individual file pages identify the artist and license. Insignia represent the divisions, not regimental affiliation badges.