Nice connections, but I don't think Gestapo fits its group, according to what I'm finding online.

Got all the groups and connections, with some guesswork and elimination. Mainly because Gestapo doesn't fit its group, as it isn't an acronym.

And Mir was a Soviet/Russian space program, nothing to do with NASA (fortunately space program was accepted, so it didn't affect the score).

"Gestapo" is listed here as an acronym.
https://acronyms.thefreedictionary.com/GESTAPO

Mir is listed here as a NASA mission, albeit a collaborative one. But I concede that I should have maybe been a bit more careful here.
https://en.wikipedia.org/wiki/List_of_NASA_missions#Crewed_missions

Thanks for playing, all the same!

Gestapo is an abbreviation built from the first few letters of the component words, as opposed to the initial letter of each word. It does seem that this is sometimes still called an acronym, but it's not the definition I'm familiar with personally.

It's nitpicking, but this distinction does make it feel different than the rest of the items in the group, which makes the connection seem weaker than it otherwise could be.

Great grid. And I'd like to defend the author, having read the comments. Firstly, words formed entirely and solely from the first letter of each word, are called Initialisms, which is a type of acronym but nonetheless a different class. Scuba would be an Initialism, whereas Radar and Sonar contain not just the first but multiple letters from their components (RADio Detection And Ranging, SOund Navigation and Ranging) and as such are just regular acronyms, just as Gestapo (GEheime STAatsPOlitzei), so if any word doesn't fit that group it's Scuba, but it does as they are all perfectly defined as acronyms. Secondly, whilst Mir was a collaboration it was absolutely a NASA mission. Admittedly it's the Mir Shuttle Program but has often been referred to by even NASA itself as the Mir Program. Excellent grid.

It's a game