Answer:
The "Order of the Day" memo that you have quoted was General Eisenhower's statement to the armed forces who were about to participate in the D-Day landing in Europe in June, 1944.
As reported by the National Archives (where a copy of Eisenhower's document is posted):
This order was issued by Gen. Dwight D. Eisenhower to encourage Allied soldiers taking part in the D-day invasion of June 6, 1944. Almost immediately after France fell to the Nazis in 1940, the Allies planned a cross-Channel assault on the German occupying forces, ultimately code-named Operation Overlord. ... His printed Order of the Day for June 6, 1944 ... was distributed to the 175,000-member expeditionary force on the eve of the invasion.