Lots of good books listed already. I'm more of a historical reader, but two novels I would recommend is:
Dune by Frank Herbert
If This Be Glory by Hasso Stachow
I don't think Dune needs an introduction considering its legendary status in the pantheon of sci-fi literature (though you could argue it's more religious/philosophy/political than sci-fi).
The real standout to me is the latter, though maybe difficult to source. It's basically a novelized version of the author's real life. The TL;DR plot to this book: boy/young man comes of age under the Nazis, is indoctrinated into the greatness of the Nazi regime/cause, joins the military, is sent to war, sours on the corruption/propaganda of the Nazi state, becomes disillusioned and ends up being "punished" by being re-assigned to the Eastern Front in a SigInt Battalion, which is basically a death sentence. (I remember it being SigInt/Comms, but maybe Engineers, been a long time since I last read it)
For any combat Vets, you'll immediately recognize some of the macabre comedy in the story. Of course, the real gem is the maturing of the main character into realizing the bill of goods his country has been sold, the horrible things they have done its behalf, and the terrible price being reaped by those who supported a regime based on lies, corruption, propaganda, etc.