My father was a USAF officer in the 1960s. He planned U-2 flights and went over the pictures taken. I have seen some of the prints first hand when I was a kid. I remember them covering the whole table (BIG prints). I also remember using a magnifying glass to look at them more closely. I do not however remember any grain. They were made with the best optics money could buy and the negatives were bigger than 8x10 inches. Still Tmax 100 has the same or better resolution but 3 times the speed of Panatomic-X.
The military has deep pockets and is reluctant to change what works. They also need to do direct comparisons to historical photos taken with the same camera and film. They can pay whatever it costs for custom runs of this film.
The reason we lost the IR films from Kodak is because the military stopped buying them. The rest of us never ordered enough for Kodak it make them.