never ever under estimate the government and military's ability to keep old systems operational well past what others consider reasonable.
anecdotal, back in the late 80s I was in the USAF. Our secure communication center was running the first model Burroughs machine to not use tubes. It was that old. It could boot from cards, paper tape, or switches. The machine was older than many people who would be assigned to it. This was closely repeated in the main data center (personnel records, inventory, and such) which had a decade old system that migrated off physical cards by 89 but still took them as images off 5.25 floppy uploaded by PC)
anecdotal, back in the late 80s I was in the USAF. Our secure communication center was running the first model Burroughs machine to not use tubes. It was that old. It could boot from cards, paper tape, or switches. The machine was older than many people who would be assigned to it. This was closely repeated in the main data center (personnel records, inventory, and such) which had a decade old system that migrated off physical cards by 89 but still took them as images off 5.25 floppy uploaded by PC)