John J. Pershing
Dwight David "Ike" Eisenhower
When he became President in April 1945, he was then in charge of all US forces.
World War I
There were over one million armed forces from the US in World War 2 including 350,000 women in the forces.
While elite units were in existence during the Second World War, the US Army Special Forces was not.
The President of the USA is also Commander In Chief of the US Armed Forces, so William McKinley was in charge.
The US joined World War 1 only in 1917 - three years after the war broke out.
Formerly the US War Department; now called the US Department of Defense.
As might be expected, the Union had a number of officers with the rank of general in the US Civil War. At the end of the war, however, US Grant was in charge of the Union's fighting forces.
British steel helmets were the only armor issued to US forces in World War 1.
The President of the USA is also Commander In Chief of the US Armed Forces, so William McKinley was in charge.
Josephus Daniels was Secretary of the Navy during World War I.