Since forts are included in the USA, there are loads of Napoleonic forts missing in the UK.
Plymouth is surrounded by them.
They have also completely omitted the entire chain of 'Palmerston's folly' Forts built around Portsmouth harbour.
https://en.wikipedia.org/wiki/Palmerston_Forts
alt Hacker News
They have also completely omitted the entire chain of 'Palmerston's folly' Forts built around Portsmouth harbour.
https://en.wikipedia.org/wiki/Palmerston_Forts