In both the original version and the remake of Red Dawn, the US — or, at least, the West coast — is invaded by contemporary communist forces (the Soviet Union in the original release, and a mostly North Korean, but also Chinese and Russian force in the remake).
In the remake especially, there's a scene where dozens of transport planes are clearly seen overflying Washington state. This made me wonder, would such an invasion tactic be remotely plausible in either the original (1984) Red Dawn or the remake?
By 1984, the US had a fairly well-developed early warning network against many types of attack on itself and its overseas assets. The States also operated Air Force bases in Japan at that point, which would likely serve as a reliable source of information about this kind of mobilization.
The US had also started using satellite reconnaissance at that point; primitive Corona satellites had been used as early as 1959, and had seen applications including surveillance of both the USSR and China. Its more-advanced successors were no doubt in use by 1984.
Currently, the US (and many of its Cold War-era allies) has a well-developed network of photographic, electronic, and radar reconnaissance and early warning satellites and over-the-horizon radars, on top of allied fleets and groups deployed in the Pacific which could surely also act as early-warning outposts.
Is there an in-universe explanation, both in the original movie as well as the remake, for how the invading forces managed to get around these measures?