Navy Ace Don Winslow worked for the Coast Guardas well. He did not exist, which made it easier to move between the two. Don Winslow appeared in two Universal serials; according to this page, he was the creation of Frank Martinek. More:
Don Winslow was a veteran of the first World War and a member of the agency of naval intelligence. The agency had Don handle threats such as villains with names such as Dr. Centaur, the Dwarf, the Crocodile, Dr. Q, and the Scorpion.
Dr. Centaur was easy to defeat; it was understood that if he broke a leg, they'd have to shoot him. Also:
He dated nurse Mercedes Colby. Mercedes was the daughter of Don's commanding officer Admiral Colby.
I'm sure that went over well.