The airplane is semi-worth seeing (I like it, but I like anything with wings), but is not as intact as the average quarry airplane and it is badly corroded (It can't compete with the *** Nomads in Rawlings and Rolesville/Fantasy Lake.) And it is cold there. But it is easy to follow the line off the tail of the plane to the deep cruiser and as boats go that one is pretty good.
If you decide to go to the plane and then decide it is too cold to continue on, you can either come back up the line or turn right and swim in the direction of the plane's left wingtip up the slope. You'll find a small sailboat and a car and if you keep going in that direction it fairly quickly shallows out and when you get to 30' again turn right and you can continue back around the side of the quarry to beach 2.
The "deep line" runs off the plane's right wingtip and goes to the winnebago, but it is a fairly long swim and is about 80 ft deep most of the way there.
Personally, I like to go to the plane, then along the deepline to the winnebago, look at what ever it is up slope from the winnebago and then turn left and work my way slwly up the wall on the way back toward beach 2. It makes a nice dive with hardly any other divers until you get mid way back up the wall about half way back to beach 2 where you start to see schools of students - or at least sense their presence in the murk they create.
Millbrook is nice in terms of shade and getting out of DC, but the viz is poor, the water is cold below about 30' they don't let you bring your scooter and there is not an awful lot to look at. Still it has a certain charm and it is at least wet and is a decent place to maintain and practice skills.
