The 9th's 1st, 2nd, and 3rd Battalions served in the 1989–1990 United States invasion of Panama, Operation Just Cause, with the 7th Infantry Division (Light).

The regiment was raised in Massachusetts, and took part in the war on the northern border, being present at the Battle of Lundy's Lane, and other actions in that area.

As a result of the Mexican–American War, in April 1847, the 9th Infantry was again organized, as one of the ten one-year regiments authorized by the Act of 11 February 1847.

Between March and November 1855, the 9th Infantry Regiment was again organized under Colonel George Wright at Fortress Monroe, Virginia.

Lieutenant-Colonel Casey with Companies D and H going to Fort Steilacoom, and was plunged into operations against the Nisqually, Muckleshoot, Puyallup, and Klickitat in the Puget Sound War.

In August 1857, Company F was detailed as escort to the Northern Boundary Commission and remained in the field on that duty nearly three years.

In 1858, during part of the wars with Native Americans in the West, the 9th was posted at Fort Dalles in Oregon Territory under the command of then Colonel George Wright.

On 17 May 1858, Steptoe's command was attacked by over one thousand Indians in the Battle of Pine Creek which triggered the Spokane – Coeur d'Alene – Paloos War.

In May 1873, six companies, A, D, E, F, H and I, were sent to the Department of Dakota for duty with the Yellowstone Expedition, escorting the engineers locating the Northern Pacific Railroad.

From the summer of 1874 to May 1876, the regiment was stationed at posts on or near the Sioux reservation in Nebraska and Wyoming and was almost constantly escorting wagon trains.

In the early part of September the entire command was without rations for a number of days, and subsisted on horse flesh and a small quantity of dried meat and fruit captured at Slim Buttes.

They remained in the field until January 1877, during the most severe part of the winter, and practically brought to a termination the Great Sioux War of 1876.

It fought in the Battle of San Juan Hill A member of the ninth infantry, Ira C. Welborn, was awarded the Medal of Honor for going under enemy fire to save a private.

In a show of gratitude from the Chinese government, the regiment was awarded two silver ingots from which the Liscum Bowl was created.

The Manchus crossed the Rhine in March 1945 and advanced rapidly through Saxony into Czechoslovakia, ending the war with many decorations including three Presidential Unit Citations.

Within hours of their arrival they found themselves under fire as their convoy made its way to the 25th Division's Củ Chi Base Camp.

The next day, a little more than 24 hours after arriving in country, Alpha company engaged the enemy in a firefight – setting the tone of regular contact that would characterize the Manchu experience for the next four and a half years.

On 22 February 1968 the Manchus closed the Katum Camp which had served as the large forward base for the 1st BDE near the Cambodian border.

After a day at Tây Ninh Combat Base to prepare, the Manchus moved out to Củ Chi and eventually arrived north of Tan Son Nhut on 25 February.

The mission was to find and destroy rocket sites that had been used to fire on Tan Son Nhut Air Base since the Tet Offensive began nearly a month earlier.

[11] Forty-nine members of Charlie Company were killed and 24 wounded in an ambush by a large communist force on Route 248 north and east of Tan Son Nhut near the small village of Quoi Xuan.

Three Manchus were posthumous recipients of the Medal of Honor, the United States' highest award for valor: Nicholas J. Cutinha, Ruppert L. Sargent and Maximo Yabes.

After its service during the Vietnam War, the 4th Battalion was transferred back to Hawaii where it was inactivated in June 1972 and reactivated under the 171st Infantry Brigade again in Alaska in August 1972.

(Camp Kitty Hawk was later renamed Camp Bonifas in memory of Captain Arthur Bonifas, who was murdered along with Lieutenant Mark Barrett by North Korean troops during the Axe Murder Incident, which resulted in Operation Paul Bunyan being conducted by the United States Army.)

Wass de Czege made it policy that Manchus earned the right to wear the belt buckle upon completion of the 25-mile road march.

In May, the 1st and 2nd Battalions along with the regimental headquarters deployed to Panama as part of a show-of-force Operation Nimrod Dancer along with other U.S. forces.

Based upon vetted reports, 2nd Battalion's Alpha Company under the command of Captain Terry Whitacker raided a residence and found an extensive weapons cache but unknown to them at the time belonged to the Nicaraguan ambassador.

The unit moved into the barracks near the 75th Ranger Battalion, adjacent to Grey Army Airfield on the main post of Fort Lewis.

Upon returning stateside the Manchu's were based at Fort Carson, Colorado, as part of the 2nd Brigade Combat Team of the Second Infantry Division.

The battalion deployed to Iraq in the spring of 2007 and engaged in combat operations in Tarmiyah, the Battle of Baqubah, and other locations throughout Diyala and Salah Ed-Din.