Well.. sounds a bit too far fetched.. if he's just a regular soldier, even if special ops, he barely has any power to change the grander scale of things. Also it doesn't sound like something a normal person would think about (change the war). Just seems like the story would be full of plot armor to get everything going the right way.
The second is.. german experiment+soul travel+ww2.. just too far fetched for me.
If it's in our world, why not settle with a "dream"? He dreamed of things all the way to his death, then woke up. Why was the dream so long and why did everything look so real? Was it a coincidence all these deja vu moments that are happening? - a lot of questions but that would be easier to digest than the german experiment thing.
Then the goal.. maybe make it more humble? Try to save some of his friends who died? If the course of the war is somehow altered as a result, sure, but that shouldn't be an idea from the mc - he's a soldier, should be close to reality.
Then again, i'm not a big fan of these kind of novels, so take what i said with a grain of salt.
Cheers!