This is a brigade-sized mechanized unit of the United States Army, originally formed in 1901 during the Philippine Insurrection as horse cavalry (more properly, dragoons/mounted infantry) and involved in the Punitive Expedition of 1916 but not World War I.
Reorganized as armored cavalry shortly after America entered World War II, the 11th was further reorganized and re-flagged as two tank battalions and a cavalry group headquarters, all of which saw action in the European Theater of Operations before being disbanded at the end of the war. One of the tank battalions and the cavalry group headquarters were reactivated as horse-mounted constabulary regiments in 1946 but with the increasing temperature of the Cold War (and increasing stability of what was becoming West Germany)the constabulary regiments were deactivated in 1948.
Reactivated in 1951, the 11th ACR served primarily as a training unit for draftees until moving to the West German/Czech border in 1957. The 11th added an aviation company in 1960, and that same year the Army re-designated cavalry battalions and companies as the more traditional squadrons and troops in order to stimulate esprit de corps. The regiment rotated back from Germany to Fort Meade in 1964.
It was in Vietnam that the Blackhorse Regiment would earn its fame, and its shoulder patch. Making an amphibious landing at Vung Tau in September 1966, the regiment began reconnaissance in force operations in the III Corps Tactical Zone around Saigon. The introduction of the 11th was controversial, since skeptics questioned the utility of mechanized units in Vietnam*, but the regiment continually developed innovative tactics, techniques and procedures that allowed them to "Find the bastards then pile on". One of these innovations was the replacement of the normal recon platoon's tanks and M114 recon vehicles with modified M113 APCs, which were equipped with additional guns to produce the Armored Cavalry Assault Vehicle. The success of the regiment's efforts can be seen in its response to the Tet Offensive of January 1968: it moved 80 miles at night through a contested area to reach Long Khanh Province, arriving 14 hours after leaving its base camp.** In the summer of 1968, Colonel George S. Patton (son of THE George Patton) took command of the Blackhorse which returned to the Saigon area, smashing a Communist force that was staging for an attack on the capital. The 11th ACR's victory was so complete that no large enemy units operated in the area for the next year. August of 1969 brought yet another innovation as an entire cavalry troop was airlifted in C-130s, giving the regiment greatly expanded strategic mobility. In April of 1970, the regiment was alerted to take part in the Cambodian Incursion, which was intended to smash Communist forces that had been using Cambodia as a sanctuary and supply base. In just 72 hours, the 11th moved into its staging area near the Fishhook, despite the 3rd Squadron having to road-march almost 90 miles. The attack jumped off on May 1 with ARC LIGHT strikes preparing the way for the Blackhorse, which was the spearhead for the 1st Cavalry Division, the 1st ACR (ARVN) and the elite 3rd Airborne Brigade (ARVN). The result was a general lack of fighting, as the Communist forces had mostly withdrawn, but huge quantities of munitions and other supplies were captured.
This was the last major operation for the 11th in Vietnam; the unit began drawing down as part of the wider U.S. withdrawal, and the 2nd Squadron was deactivated in-country on March 7, 1972.
It was not inactive for long. In May 1972, the 14th ACR was reflagged as the 11th, and the Blackhorse unfurled its colors again in Germany, this time in the critical Fulda Gap. The 11th had the twin missions of defending the Gap against Warsaw Pact invaders in wartime, and in peacetime, watching the 238 miles of the Inner German Border. Modernization and reorganization had increased the size of the regiment to over 4600 troopers, over four times the original strength of the regiment in 1901. Part of the increase was due to the Fourth Squadron, which included 74 helicopters, and the combat support squadron, whose maintenance troop was the largest in the regiment with 366 troopers. This critical border mission came to an end on November 9, 1989 when the Berlin Wall came down and with it, the Communist regime in East Germany. The regiment officially closed its border observation posts on March 1, 1990.
The 11th did not take part in the First Gulf War as a unit, though scout platoons from E and K troops were attached to other units. The remainder of the regiment arrived in June 1991 and was tasked with the defense of Kuwait; it returned to Germany in September 1991 and was deactivated on October 15, 1993, only to be reactivated at Fort Irwin on October 16 1994 as an Opposing Force training unit.
The Regiment once again did not operate as a regiment in the Second Gulf War. Its 58th Engineer Company was attached to the 2nd Brigade/10th Mountain Division in June 2004, the 2nd Squadron joined the 155th Brigade (Mississippi National Guard) in Babil Province in December 2004, and the 1st Squadron went to Baghdad in January 2005 where it served under several different brigade combat teams. Meanwhile, the regimental headquarters also deployed that month, going to Mosul where it became the division HQ for Multinational Force Northwest. Back at Fort Irwin, the Support Squadron kept the home fires burning at the Regimental Rear Command Post, while the 1/221 Cavalry of the Nevada National Guard took over the OPFOR mission until the return of the 2nd Squadron from Iraq in January 2006. The 1st Squadron is currently in Afghanistan as part of a Provincial Reconstruction Team.
*Aside from the mistaken (though popular) perception that South Vietnam was mostly rice paddies and jungle, there were more legitimate concerns as to whether the increased logistical "tail" of mechanized units was worth the increased firepower and survivability.
**David Drake's SF novel Rolling Hot is a fictional version of this action. Drake was an interrogator assigned to the 11th ACR, and his Hammer's Slammers stories are often based on the regiment's battles in Vietnam.