Makes me think of an MT "Hard Times" style adventure -

The formerly TL15 planet has slid down the scale to TL9, and most of
the subsector has slid 3TLs as well, to between 5 and 8...

However, the enemy never bombed the Museum... since nobody remembered
the TL 10 warship on display there.
Now, it's cutting edge for the PC's homeworld, and they have to quest
across the system getting parts, bringing it online, and then using it
as the flagship of a new fleet that's going to bring sanity back to
the subsector.