The 15th Marines was first organized on November 26, 1918, as an infantry regiment.

Having been organized for possible deployment to Europe in the event that hostilities resumed, the 15th Marines remained on garrison duty in the Dominican Republic.

It was formed by combining Pack Howitzer Battalions from the 4th, 22nd, and the 29th Marines.

The Regiment was withdrawn from Okinawa after it was declared secure in July 1945 and was redeployed to Guam to prepare for the invasion of Japan.

The 15th Marines remained in China until its deactivation on March 26, 1946.