If our high command knew the whole Nazi story, Holocaust, etc., and understood how bad letting the Soviets take Eastern Europe would complicate the upcoming post-war world, then the war would be over very quickly.
Berlin would be incinerated by lunchtime and the rump government would be trying to get organized enough to surrender by sunset. Especially so when you consider that by D-Day in 1944 a lot of high ranking Nazis had become anti-Hitler at least in secret. The folks outside Berlin would be real anxious to stop the fighting.
If we weren’t willing to use nukes first we’d still be bunker-busting the crap out of their HQs. EW would terminate their entire national command and control system except for motorcycle couriers and carrier pigeons. If we let them keep radio we’d break all the ciphers trivially and read their comms from end to end.
The biggest problem the modern air arms would have is that we simply don’t have enough airplanes to kill all the juicy essentially undefended targets. But unlike in WWII we don’t need to drop 10,000 tons of bombs over a week to wreck a factory. Instead we send in 2 jets one time and actually hit the place.
The Navy would be similar. Shortly after a U-boat surfaces at night it simply explodes. They can’t detect our radars nor our incoming ordnance. Nor do anything about it if they do. As with the air forces, we don’t have the raw numbers to be everywhere. But anywhere we are, they’re not. At least not anymore. Zero of their spotter planes will return from their first mission. The Nazi surface navy, such as it was by 1944, wouldn’t fare any better. Nobody would realize they were in danger until they started exploding. You just can’t fight what you can’t see.
The Army will have it rougher, but not that much rougher. Between artillery and night vision it’ll be like the Blitzkrieg was against the Polish cavalry in 1939 but in reverse. They can’t see, think, decide, move, or shoot even half as fast as we can. Nor can they do it 24 hours a day rain or shine.
Again the biggest problem we face is compared to the sheer physical size of the German army, we just don’t have that many men or machines. We utterly dominate wherever we are. But there’s lots of places we just can’t be. Fortunately modern air power can hold a flank pretty well. Keeping our supply lines secure from pincer attacks is probably the rate-limiting step in the advance.
Unlike in WWII we may not really need to be doing strategic bombing, other than of military HQs and staging yards. We’re going to win by driving our spearhead into their capital in a few days tops. The war of strategic factory destruction and materiel attrition we fought last time just won’t be necessary.
Instead of the ginourmous multi-fronted war back in real 1944 this time the Army will drive their forces eastwards across a relatively narrow (WAG) 300 mile front and the air arms will be tasked to keep any serious flank attacks at bay. Even now that’d be a tall order in the low stratus of a European winter. In June it’d be almost fun.
The modern DoD is at its best when it can plan. So the best thing to do might be to materialize the modern US into the scenario in early May 1944 then spend about a month (or two) getting the whole intel / mapping / targeting system aligned with the current Nazi reality. While moving the heavy / slow forces from CONUS over to be in position for D-Day. Then when we’re set up, drop the flag and drive at full speed to (what’s left of) Berlin.
And this time keep going until we arrive at the Soviet border.
Individual DoD members are most certainly at risk here. Nobody is bulletproof just because your side is assured of winning. But the casualty counts are gonna be real lopsided. Just like in Iraq.