RAF Hercules Astrodome

Alright, I’m new here, so be gentle with me!

I’m in New Zealand, and over the weekend we had an RAF C130K visit Wellington Airport, presumably on British High Commission business, as there were no military exercises with the RNZAF at that time. A number of people noticed that it had an Astrodome fitted and wondered why. They don’t seem to be fitted to all RAF Hercs; certainly none of the “J”s, and I can’t recall ever seeing one on any other air force’s Hercs, [and I have 25 years air force service behind me!], which raises the questions:

Does anyone know why they were fitted in the first place? Surely not for navigation, even in 1968!

Were they removed from some aircraft because evidently , today, not all aircraft in the fleet are so fitted?

Cheers

Sam