Zane embarked in the transport Henderson on 19 January 1918, bound for France. By that point a major, Zane served his first tour of duty "over there" in the Bourmont, France, training area, with the 6th Marine Regiment. Then, he went to the front lines, southeast of the famous battlefield at Verdun, where he remained from mid-March to mid-May. After moving with his unit to Vitry-le-Francois and then to Gisors-Chaumont-en-Vexin, Zane and his companions received urgent orders sending them to the Chateau-Thierry sector. Major Zane participated in the fighting in the vicinity of Belleau Wood, when the untried marines came up against the 461st Imperial German Infantry, a unit that Colonel Robert D. Heinl called "the largest single body of combat-seasoned regular troops which Marines had confronted since Bladensburg." He recevied the Navy Cross for his actions during the fighting at Bouresches, where "he displayed such bravery as to inspire the garrison to resist successfully a heavy machine-gun and infantry attack by superior numbers." He also received the Army Distinguished Service Cross for the same action.

Zane took part in the second phase of the assault, when the 2d and 3d Battalions, 6th Marines, entered the wood, and remained in action through the entire period of fighting. Tragically, Zane was wounded and shell-shocked on 26 June. Following his partial recovery, he served as Provost Marshal at Le Havre. Developing complications, however, Zane died of influenza after ear surgery on October 24, 1918. He is buried at the Somme American Military Cemetery, Bony, France.

Image of Randolph T. Zane, from Los Angeles Evening Express, 13 November 1918.