These systems are designed to do one thing and do it well, without error. They have been in place a long time. Because they are old does not mean they are not

These systems are designed to do one thing and do it well, without error. They have been in place a long time. Because they are old does not mean they are not secure. Much like the Apollo mission computers are often quoted as being "less powerful than a calculator" does not mean that they do not work. Many military computers are not impressive from a hardware standpoint because they don't have to be.