https://www.history.com/this-day-in-history/allies-argue-over-u-s-troops-joining-battle-on-western-front?cmpid=email-hist-tdih-2021-0 [login to see] 1&om_rid= On March 23, two days after the launch of a major German offensive in northern France, British Prime Minister David Lloyd George telegraphed the British ambassador in Washington, Lord Reading, urging him to explain to U.S. President Woodrow Wilson that without help from the U.S., “we cannot keep our divisions supplied for more than a short time at the present rate of loss.This situation is undoubtedly critical and if America delays now she may be too late.” In response, Wilson agreed to send a direct order to the commander in chief of the American Expeditionary Force, General John J. Pershing, telling him that American troops already in France should join British and French divisions immediately, without waiting for enough soldiers to arrive to form brigades of their own. Pershing agreed to this on April 2, providing a boost in morale for the exhausted Allies. On May 2, the second day of the meeting, the debate continued, with Pershing holding his ground in the face of heated appeals by the other leaders. He proposed a compromise, which in the end Lloyd George and Clemenceau had no choice but to accept: the U.S. would send the 130,000 troops arriving in May, as well as another 150,000 in June, to join the Allied line directly. He would make no provision for July. This agreement meant that of the 650,000 American troops in Europe by the end of May 1918, roughly one-third would see action that summer; the other two-thirds would not join the line until they were organized, trained and ready to fight as a purely American army, which Pershing estimated would not happen until the late spring of 1919.
Course by the time those additional troops were ready the Armistice was completed. I didn't know this fact about troops being withheld from combat. I thought the units were, pretty much, pushed to the front lines as soon as they set foot in France.