Guess what this is??

A rare entry to Derelict Thursday for me.
Here is a clue. I was out this afternoon for a meeting on a local airfield where this building was in the process of being demolished. There was a chap in a hi viz jacket taking pictures, it turned out he was documenting the demolition and redevelopment of the site and so told me about this building and it's very specific purpose. Can you work out what it was used for???

Landed two new contracts today, this is most excellent news (thanks if you are reading). The meeting this afternoon was however pure comedy due to miscommunication, traffic and general fecklessness we ended up in the clients office whilst the client ended up in the partner agencies office 30 miles away. Luckily skype was on hand so the meeting went ahead anyway.