Compass Swings
Hi,
I know you said Major, I have been racking my tiny little Ops Bird brain and all I can come up with is RAF Leeming. I know Cobham use it and also Sea Kings from Yeovilton and Culdrose. So depending on the size of frame you want to check( restricted by Fire Cover and LCN) It may or may not be an answer for you.
Cheers Ops Bird