Just thinking about some info that could be provided when you look at individual vehicle pages...
Similarly how you can see how many miles the vehicle has driven, how about how many hours the vehicle has been on missions for?
There's probably a more simple way of wording it, but pretty much how long in total the vehicle has spent completing missions. Personally, I also think this time should include the travel time to and from the scene - but that can also be open to discussion...
Just thought it would be a cool little addition!