Judging by the size of the wing and the placement of the roundel and the bullet holes, I'd say it is the discarded wing of a RCAT. Remotely Controlled Aerial Target. They are a modular built, propeller driven, recoverable aircraft used by the US military to train anti-aircraft batteries on both land and sea. My guess is that this wing of a Navy RCAT that was recovered and deemed unrepairable and discarded or crashed and lost at sea, judging from your narrative. The US Army classified them as recoverable, The Navy may have classified them as expendable do to the difficulties of recovery at sea but I can't say for sure.
Although it may not be one of the vertical stabilizers off of one of Doolittles' Raiders B-25's, it's still an interesting artifact. I had an opportunity in the early 80's to try my hand at shooting one down. I was using a .50 caliber machine gun mounted on a armored personnel carrier (APC). I think it ran out of gas about the same time I ran out of ammo! I don't think I touched it. They were quick and very agile. You'll notice the wing in the picture has no ailerons. They only had rudder and elevators with a lot of authority and maneuvered more like a bat than an airplane. I figure if I did hit it, it must have flown into the bullet! Nowadays it's CRT's, joysticks and Gattling guns. RCAT (the company) is still in business today.
Cheers,
Dave