Great Museum!
It's a great little museum. My dad took me there when I was little (we loved quite close so went a few times) and I was peering up the ladder of of Mossie prototype when one of the volunteers came up to me and said, "It's quiet, you can jump in and have a look if you want." Made my day! The de Havilland factory in Hatfield also gave birth to the Hatfield Polytechnic (now University of Hertfordshire) which still has a well respected engineering department. There is a statue outside dedicated to Geoffrey de Havilland. When the airfield at Hatfield closed (plunging the town of Hatfield into a decline it took ages to recover from) the university bought some of the land and opened a big campus there. The original hanger is now a sports club. You can play tennis where great airliners and fighters were once built which I think is kinda sad....
(extra geek fact: Salisbury Hall was also home, for a short time, to Sir Nigel Gresley, designer of the Flying Scotsman and Mallard (fastest steam engine in the world).)