Approved 23 March 1923, the 21st Infantry Regiment Distinctive Unit Insignia (DUI), often referred to by Soldiers as a “unit crest,” is chock-a-block with symbolism from the unit’s history up to that point. A cedar tree is a reference to the Regiment’s baptism by fire at the Battle of Cedar Mountain in 1862. Above it is a five-bastioned fort, an allusion to the Regiment’s service in the V Corps during the War with Spain (V Corps’ insignia featured such a fort). Glowing behind the fort is a Katipunan, symbol of the Philippine insurrectionists. At the top are crossed red arrows, symbolic of the unit’s participation in the Indian Wars, along with a rattlesnake skin, an Indian emblem signifying war.
The Distinctive Unit Insignia is worn by all Soldiers (except General Officers) in units that have been authorized to be issued the device. It is worn centered on the shoulder loops of the Army Green Service Uniform (AGSU) and the blue Army Service Uniform (ASU, Enlisted only) with the base of the insignia toward the outside shoulder seam. DUIs are not worn on the Dress variations of either uniform, however.
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For over 100 years, the 21st Infantry Regiment—originally formed as the 2nd Battalion, 12th Infantry Regiment on 3 May 1861—has been faithful to its simple yet powerful motto, “Duty.” Activated the following year, the units of the Regiment were almost immediately sent into battle at Cedar Mountain, a bloody affair commemorated on the Regiment’s unit crest. In total, the Regiment would take part in a dozen Civil War campaigns, eight Indian War Campaigns, the Battle of Santiago during the War with Spain, and four campaigns during the Philippine Insurrection—all before the end of the first decade of the 20th century.
During World War II, the Regiment would take part in five campaigns in the Pacific Theater, with two of the five streamers featuring Arrowheads because the unit took part in assault landings; these were augmented by a Philippine Presidential Unit Citation. Nicknamed “Gimlets” by now for reasons that today are somewhat muddy but probably quite clear at the time, the Regiment earned credit for eight Korean War campaigns (and pairs of the Republic of Korea Presidential Unit Citation and Presidential Unit Citation) and an astonishing 14 campaigns in the Vietnam War, where its service was recognized with a Valorous Unit Award and Navy Unit Commendation.
Since 1990, the Regiment has seen action in the First Gulf War and in campaigns in support of Operation Iraqi Freedom and Enduring Freedom, with the total number of War on Terrorism campaigns yet to be determined. Only two of the Regiment’s battalions, the 1st and the 3rd, are still active as of 2023. The 1st Battalion, 21st Infantry Regiment is assigned to the 2nd Infantry Brigade Combat Team, 25th Infantry Division, while the 3rd Battalion is part of the 11th Airborne Division's 1st Brigade Combat Team.