The plane that strafes the truck and later the ship is a B-25 Mitchell, an American medium bomber, not an enemy aircraft.
The story is set in 1953 but one of Dennison's books is an edition first published in 1962.
The term "over" used with radio (or telephone) communications means "I have finished speaking for the moment, but am expecting your reply - go ahead". "Out" means "I have finished, and this communication is finished; don't reply." "Over and out" means, "Reply, but don't reply" (and "I'm a jerk who doesn't know correct communications procedure)."