According to Robert Vaughn in his biography, during the shooting of this with Kathy Kersh, he proposed to drive her home after a day's work. She then invited him for a drink. He accepted, but just after he entered the living room, Vince Edwards - who was her husband at that time - appeared in front of them and there was a severe argument between husband and wife, at which point Vaughn quietly left.
The race car featured is a Shelby Cobra.
This was the second and final appearance of Dr. Egret, which like Thrush, is the name of a bird. She was previously played by Lee Meriwether in "The Mad, Mad Tea Party Affair". The fact that she wore a disguise implies they either intended for different actresses to play her in the future or that Meriwether would later reprise the role.
The title of this episode appears to be a play on "The Guns Of Navarone", Alistair MacLean's 1957 novel about World War II which was made into a popular film in 1961.