Mr Roosevelt originally delivered the prayer to the US nation when he was president on the evening of D-Day - 6th June 1944.
Donald Trump joined the Queen and other members of the royal family, world leaders and hundreds of veterans to honour those who took part in the D-Day landings 75 years ago.
Mr Trump stood on the stage on Southsea Common next to the Portsmouth Naval Memorial and read: "Almighty God: Our sons, pride of our nation, this day have set upon a mighty endeavour, a struggle to preserve our republic, our religion, and our civilisation, and to set free a suffering humanity.
"They will need Thy blessings. For the enemy is strong.
"He may hurl back our forces but we shall return again and again and we know that by Thy grace, and by the righteous of our cause, our sons will triumph.
"Some will never return. Embrace these, Father, and receive them, Thy heroic servants, into Thy kingdom.
"And, O Lord, give us faith. Give us faith in Thee; faith in our sons; faith in each other and faith in our united crusade.
"Thy will be done, Almighty God. Amen."
More than 150,000 troops from the UK, the US, Canada, and France attacked German forces on the coast of northern France, on 6th June 1944.
It was the biggest combined land, air and sea operation in history and ultimately liberated German-occupied Western Europe.
In total, 4,400 from the combined allied forces died on the day.
There were 4,000 - 9,000 German casualties and thousands of French civilians died.
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