PB,
Just about every squadron has an aeroplane that proves to be more troublesome than all the rest. Nobody can quite work out why this is; perhaps they were built on a Friday afternoon or Monday morning!
As a result they spend most of their time in the hangar or HAS and get 'robbed' of all the good bits to keep the rest of the squadron's aeroplanes flying, until there is virtually nothing left to rob. When the replacement parts arrive they don't get fitted because you know you will be robbing them again! So they just sit there gathering dust with all the access panels removed and looking very sad. They are often called 'Christmas Trees' and when I was at Wattisham on 23 sqn we had a Phantom that we did indeed, decorate at Christmas time, complete with lights!
So your father would definitely have had a Christmas Tree on all the squadrons he worked on.