How many americans served on the front by the end of the war, and how many died?

The correct answer is:

1.3 million served and 50,000 died.

American losses in World War I were modest in contrast to those of other belligerents. The United States lost further soldiers to disease (63,114) than to actual warfare (53,402).  The influenza epidemic of 1918 was key to this situation. Furthermore, earlier in the war European doctors had obtained knowledge that helped Americans decrease deaths from chemical weapons, shell shock, and infected gunshot and shrapnel wounds.