Off topic, but your thread, David.
In the mid-sixties, F-105s were shooting up ships along the North Vietnam coast with their gatling gun. PACAF got wind of it and the directive came down, "No more shooting at ships! You'll kill a Russian!" (The 104s out of Da Nang were firing sidewinders at them too)
Wing: Okay, no ships. How 'bout boats ?
PACAF Reply: Boats are okay to shoot at.
Wing: Fine. Boats, not ships. Now, what's the difference?
PACAF reply (after much reflection): Ships have masts, boats don't.
You can see where this is going-- Lead spots a freighter offloading, rolls in and saws it's masts off with his gun. Two calls "Boat!", and lights it up.
This was related to me by an F-4C driver at Ubon TAFB in 1968. I believe the ground attacks ended before PACAF learned about them, and when the primary 105 mission became Hanoi, nobody had enough fuel coming off the target to stay low.
As an aside, Ho Chi Minh's hometown was off-limits by order of the white house, but F 4s periodically engaged in knocking down huts with low-level mach 1+ shock waves and the occasional "Oops!" bomb. Twenty-something fighter pilots tend to be insubordinate.