Following action in the Civil War and the western frontier, the 15th Infantry Regiment's legacy was deeply shaped by its service in the Far East. By mid-1912, the 1st and 3rd Battalions, along with the regimental headquarters, were established in Tientsin, China. Tasked with protecting Western civilians and interests as part of a multinational effort following the Boxer Rebellion, the regiment spent over two decades in China. This prolonged overseas duty earned the unit the moniker of the "China Regiment". It was during this period that the regiment adopted the Chinese dragon on its regimental crest and the Pidgin English motto "Can Do," a phrase that encapsulated the battalion’s readiness to execute any mission. The 3rd Battalion finally left China with the rest of the regiment in early 1938, returning to the United States.

Assigned to the 3rd Infantry Division in 1940, the 3rd Battalion soon found itself thrust into the crucible of World War II. The 15th Infantry Regiment participated in amphibious landings in North Africa, Sicily (Operation Husky), Italy, and Southern France, fighting its way into the heart of Germany. The regiment became renowned for its battlefield tenacity and produced sixteen Medal of Honor recipients during the war, including Audie Murphy, the most decorated American combat soldier of the conflict. Shortly after the end of World War II, the battalion answered the call in Korea. The 15th Infantry notably covered the withdrawal of X Corps from the frozen Chosin Reservoir in 1950, and later fought near the 38th parallel. In 1953, elements of the 15th Infantry successfully defended Outpost Harry, a strategic position in the Cheorwon Valley, holding the line for eight nights against staggering assaults by Chinese forces.

During the Cold War, the Army underwent multiple force reorganizations that led to temporary inactivations. However, the 3rd Battalion, 15th Infantry was reactivated in August 1989 at Fort Stewart, Georgia, joining the 24th Infantry Division. It rapidly deployed to the Middle East for Operation Desert Shield and Desert Storm in 1990, helping to liberate Kuwait from Iraqi forces. The 1990s demanded extreme versatility from the "Can Do" battalion. In 1993, the 3rd Battalion deployed three companies to Mogadishu, Somalia, conducting combat operations for Operations Restore Hope and Continue Hope. The following year, one company deployed to Haiti to support Operation Uphold Democracy. The battalion later served as an element of Task Force Eagle in Bosnia from 2000 to 2001 in support of Operation Joint Forge.

With the onset of the Global War on Terrorism, the 3rd Battalion once again proved its mettle. Serving under the 3rd Infantry Division, the battalion formed part of the spearhead into Iraq during Operation Iraqi Freedom in 2003, and completed a subsequent tour in 2005-2006. In early 2013, nearly the entire 3rd Battalion deployed to Afghanistan, conducting intense operations from Combat Outpost Soltan Kheyl in the rugged Wardak Province.

Today, following the 2015 inactivation of its sister battalions, the 3rd Battalion stands as the sole remaining active unit of the historic 15th Infantry Regiment. Stationed at Fort Stewart, Georgia, as part of the 2nd Brigade, 3rd Infantry Division, the 3rd Battalion, 15th Infantry continues to train for future conflicts. From the shores of Sicily to the deserts of Iraq, the soldiers of the 3-15 IN have consistently lived up to their historic mandate, proving in every era that they truly "Can Do".