Before you guys get too carried away telling him he's wrong, do a bit more digging. May 1938 the 2nd BG and their early 17s as part of proving they could be effective in defending the US, flew a mission out to intercept an Italian Liner by the name of Rex. Col Old, (Robin Old's father) lead the flight and Curtis LeMay was lead navigator. They successfully intercepted the ship 700 miles out.
This did not go over well in those pre-war days when the services were fighting for money and the Navy raised holy hell to the point the Air Corps was limited to only 100 miles out to protect the coasts as the Navy saw it as their job to do so beyond that limit.
So yes, Coastal Defense was a part of the B-17 mission.
The 2nd BG finds the Rex