After a brief stop, the regiment crossed the English Channel from Southampton to Le Havre, France and then moved by train to La Courtine.

In preparation for the St. Mihiel Offensive, the 2nd Battalion rejoined the 321st, and the regiment moved into forward gun positions constructed with the assistance of the division's infantry.

Beginning at 0100hrs on 12 September 1918, the 321st participated in a four-hour preparation, consisting of counter-battery fires on 16 German batteries and other positions.

After the offensive started, the regiment also fired on "fugitive targets", and Battery C destroyed a German airplane that had made a forced landing.

On 13 September, the 321st and its sister 320th Field Artillery fired 10000 rounds in support of a raid by the 327th Infantry in the Bois Frehaut.

After participating in a truncated preparation due to the late arrival, the regiment fired in support of the infantry throughout the day.

On the night of 21–22 October, the 1st Battalion, 321st withdrew to new positions, and the regiment settled into a period of "stabilized warfare" until 1 November.

During this period, the regiment fires light harassing schedules at night and continued close support missions to the infantry.

Beginning 26 October, the battalion moved one gun per battery into forward positions and conducted adjustments in preparation for a new offensive, scheduled for 1 November.

On the morning of 2 November, the attack resumed at 0800 hours, and the 321st moved forward and established a regimental command post in the town of Imecourt.

The 2/321 assigned two accompanying guns to the brigade's two infantry regiments, but had difficulty acquiring targets due to the lack of German resistance.

[8] The 321st Field Artillery sailed back to the United States in the spring of 1919 and was demobilized at Camp Dix, New Jersey, on 26 May 1919.

The War Department initially did not assign 155 mm howitzer regiments to infantry divisions in the reorganization of the early 1920s, and the 321st remained inactive.

A Gold color metal and enamel device 1+1⁄8 inches (2.9 cm) in height overall consisting of a shield blazoned: Gules, two lion's paws issuing out of the dexter and sinister base points chevron-ways Or.

[11] On a wreath Or and Gules, a cannon barrel palewise Sable winged Argent behind a lion sejant affronté with two heads addorsed of the first armed and langued Azure grasping in each forepaw a round of the third and surmounted by an escutcheon per pale Gules and of the fifth an annulet Argent, on a chief of the like three fleurs-de-lis Azure.

The winged cannon stands for the former designation of the organization as a Glider Field Artillery Battalion and its assignment during World War II to the 101st Airborne Division.

The red and blue escutcheon is from the arms of Bastogne; the annulet represents the enemy encirclement of that objective and refers to the unit's distinguished action in its defense during World War II.

It was redesignated for the 518th Airborne Field Artillery Battalion and amended to delete the Organized Reserves crest on 26 September 1951.