system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why replace old battleships/aircraft carriers but not the b52?

Old time/battle tested warships are scrapped to make way for new ships that bristle with brand new tech that isn't battle tested, but they keep using the b52 bomber from 55 years ago?

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Edit; Thanks for all the comments, I was thinking aircraft carriers mostly, it makes sense that actual battleships are outdated but the superstructure of an aircraft carrier should be able to be modified in the same way that a b-52 is modified over the years, also didn't consider the erosion from exposure to salt air and seawater.
gpt
You had better believe there is new tech in the B-52 of today. But the airframe, the flying around bit, hasn't really changed in 50 years. What does it need to do now that it didn't back then?

Battleships on the other hand have changed quite a lot. Instead of slugging it out with giant cannons and meter thick armor, they now launch missiles and have small, rapid firing cannons for close defense. You can't retrofit a battleship with 3 meter thick armor and 20 inch guns into one that has 6 inches of hull and missile bays.