The term unconditional surrender was never used in the agreement. I doubt that he cared at all about the Japanese saving face. Truman feared the losses from a ground invasion. After all, he knew full well that we had a limited A bomb stockpile. Regardless of any later spin (and that's all it was), his New Deal advisors were quite upset at what they perceived a cave.
But the Japanese were not going any where. They were trapped on their island. We could have waited a year...two for an unconditional surrender. McArthur was the one that was able to transform that situation and help them save face and make the a valuable partner for the next 60 years.
And just how many people read the actual instrument of surrender? A tiny fraction of the people who heard Truman's speech on the occasion:
My fellow Americans, and the Supreme Allied Commander, General MacArthur, in Tokyo Bay:
The thoughts and hopes of all America--indeed of all the civilized world--are centered tonight on the battleship Missouri. There on that small piece of American soil anchored in Tokyo Harbor the Japanese have just officially laid down their arms. They have signed terms of unconditional surrender.
I doubt that he cared at all about the Japanese saving face. Truman feared the losses from a ground invasion.
Those aren't unrelated considerations. "Saving face" is a very, very big deal in Asian cultures, and the Japanese took "death before dishonor" to a fanatical extreme. Allowing the Japanese to save face allowed them to surrender.
A public diplomatic win with secret conditions isn't unusual -- the Cuban Missile Crisis resulted in Soviet missiles being loudly removed from Cuba, and NATO missiles being quietly removed from Turkey. The missiles in Turkey weren't needed anyway, but it let Khrushchev save face with the Politburo.
Regardless of any later spin (and that's all it was), his New Deal advisors were quite upset at what they perceived a cave.
And Truman was pragmatic enough not to worry whether he was seen as "caving" to an utterly defeated enemy whose new constitution we were writing for them.