The 15th fought in the Champlain Valley campaign in autumn 1814 at Plattsburgh, and participated in General Dearborn's offensive in Ontario in October, and took part in many smaller battles that same year.

As companies of the 15th arrived at Vera Cruz, they moved inland to join General Winfield Scott's army advancing on Mexico City.

The regiment fought in the battles of Contreras and Churubusco, as well as smaller engagements before storming the walls of Chapultepec in Mexico City.

Following garrison duty in Mexico City and Cuernavaca, the regiment returned to the United States for inactivation in August 1848.

Its headquarters first in Wheeling,[3]: 42–48  West Virginia then Cleveland, Ohio, then on to Newport Barracks, Kentucky and finally ending up in Fort Adams, Rhode Island in September 1862.

By the end of the Civil War, the regiment had fought in 22 major engagements, including Murfreesboro, Chickamauga, Chattanooga, and Atlanta as a part of Brigadier General John H. King's Brigade under Gen. Richard Johnson's Division, XIV Army Corps of the Army of the Cumberland.

Porter spent little time in actual command of the regiment after its original organization, as he was promoted to brigadier general of volunteers in August 1861.

Porter was succeed as regimental commander by Colonel Oliver L. Shepherd who served as such from January 1863 to December 1870.

While at Fort Sheridan the regiment played a vital role in containing the Chicago Railway Riots in July 1894.

During the latter part of the month, the Battalion reconnoitered and skirmished continuously over the same terrain where the 9th Infantry had lost 100 men killed in action (including their regimental commander, Colonel Liscum).

About 1 September, Companies A, B, and D were assigned the duty of escorting junks carrying supplies up the Pei Ho River to Peking.

Through the latter part of November the battalion was engaged in almost daily expeditions against small bands of Boxers in nearby villages.

After five months of heavy scout work the company left for San Jose de Lagamoy, where it was engaged in tracking down bands of headhunters.

Between 14 April and 31 July 1902 the company occupied Nueva Cacera (now Naga), Sorsogon, Bulan, and Point Binatao.

The 2nd Battalion, which had remained in New York, did not appear in the Philippines until February 1902, just in time to turn around and return with its outfit in September to the United States.

Before this removal, the regiment's entrants won first, second and fourth honors in the individual competition, and five of its six contestants made the ten-man Army Rifle Team.

The enlistments of 500 men had expired during 1908, and green recruits had filled the regiment at its home station in Utah and took part in a banquet given in their honor by the officers.

[14] By mid-1912, Headquarters, the Band, and the 1st and 3rd Battalions were established at Tientsin in China as part of a multinational colonial effort designed to protect Western civilians during the Boxer Rebellion; the 2nd in the Philippines.

The mission of the regiment became difficult to define, and in the course of time the unit itself was transferred to the control of the State Department.

[14] In line with new doctrine on organization, three provisional companies, Headquarters, Supply, and Machine Gun, were formed during August 1914, and in 1916 they were made permanent.

Christmas Day, 1925 was very tense, for 5,000 troops belonging to Feng Yuxiang, a warlord from the north, entered the area.

As Finney mentions, The Chinese Memorial Gate now at Fort Moore was presented to the regiment in 1925 by local villagers in gratitude for being protected against the troops of warlord Feng's army.

The 15th Infantry Regiment's casualties during World War II included 1,633 killed, 5,812 wounded, and 419 missing in action.

These units maintained their "battle skills" by several deployments to Grafenwoehr and Hohenfels training centers as well as several REFORGER exercises.

From 2000 to 2001, 3rd Battalion, 15th Infantry deployed to Camp McGovern in Bosnia as an element of Task Force Eagle in support of Operation Joint Forge.

In early 2013, nearly all of 3rd Battalion deployed to Wardak Province, Afghanistan operating from Combat Outpost Soltan Kheyl and FOB Airborne.

The acorn is repeated four times to commemorate the four major engagements in which the regiment participated: Murfreesboro, Chickamauga, Chattanooga, and Atlanta.

The Chinese dragon, in gold metal, is indicative of the regiment's service in China during the Boxer Rebellion from 1900 to 1938, of which the period after 1912 was continuous.

The sunburst, triangle, and devices atop the coat of arms is symbolic of the Katipunan flag of the Philippine Insurrection.

[22] Without inscription The 15th Infantry didn't receive any separate Presidential Unit Citation for World War II.