From a press conference in Honolulu, July 29, 1944:
"THE PRESIDENT: Still is with everybody. There has been a good deal of complaint among some of the nice, high-minded people about unconditional surrender, that if we changed the term "unconditional surrender," Germany might surrender more quickly.
Mr. Churchill and I have made no modification of the terms of unconditional surrender.
They complain that it is too tough and too rough. I will explain it a little this way.
Back in 1865, Lee was driven into a corner back of Richmond, at Appomattox Court House. His army was practically starving, had had no sleep for two or three days, his arms were practically expended.
So he went, under a flag of truce, to Grant. Lee had come to Grant thinking about his men. He asked Grant for his terms of surrender.
Grant said, "Unconditional surrender."
Lee said he couldn't do that, he had to get some things. Just for example, he had no food for more than one meal for his army.
Grant said, "That is pretty tough."
Lee then said, "My cavalry horses don't belong to us, they belong to our officers and they need them back home."
Grant said, "Unconditional surrender."
Lee then said, "All right. I surrender," and tendered his sword to Grant.
Grant said, "Bob, put it back. Now, do you unconditionally surrender?"
Lee said, "Yes."
Then Grant said, "You are my prisoners now. Do you need food for your men?"
Lee said, "Yes. I haven't got more than enough for one meal more."
Then Grant said, "Now, about those horses that belong to the Confederate officers. Why do you want them?"
Lee said, "We need them for the spring plowing."
Grant said, "Tell your officers to take the animals home and do the spring plowing."
There you have unconditional surrender. I have given you no new term. We are human beings—normal, thinking human beings. That is what we mean by unconditional surrender."
http://www.presidency.ucsb.edu/ws/index.php?pid=16539