It was Karl Malden's idea to have his character speak in a different accent constantly. He thought it would be an amusing gimmick.

Unlike the novel, this takes a light-hearted, spoofy style with Dean Martin essentially playing himself. The Matt Helm of the novels is a much darker creation.

The large, white hovercraft appears to be a Saunders-Roe Nautical 6 (SR.N6). The smaller hovercraft appears to be the Britten-Norman "Cushioncraft" 5 (CC5). There was one CC5 built which capsized during tests off of Priory Bay.

This was originally intended to be shot on location but Dean Martin refused to travel to Europe.

Sequel to The Silencers (1966) and the second of four Matt Helm movies to be made.

Continuity

When the hovercraft first arrives on Wall's island, it comes to a rest parallel to the shore on a concrete pad surrounded by gravel. In the very next shot it is in an entirely different location, concrete everywhere, no gravel, next to an ancient fort wall and facing the ocean.

When the hovercraft returns to the mainland, it is shown coming out of the sea and moving over the beach. The action cuts back to the discotheque, but when it returns to the hovercraft, it is shown still in the sea and heading to the beach.

During the car chase up the hill, Matt's car is viewed at each switchback corner through a fish-eye lens. The bad guy's car is not to be seen, even though views out Matt's back window. Shots immediately before and after the chase show the car in hot pursuit, right on their tail.

The number of mini-spears that Julian Wall holds in his hand for the spear gun changes between shots, from three to two.

The parachute that Matt deploys onto the pursuing car is shown opening twice.



Revealing mistakes

When the hovercraft arrives at Julian Wall's island for the first time, as everyone disembarks, their heads are cut off when they pass behind the matte of the water that is overlaid onto the scene.

When Matt test-fires the silenced ten-second-delay gun, he starts the count at six right after pulling the trigger and it then goes off at the ten-count (actually only a 4 second delay). The second time he uses the gun, in the castle, it does take the full 10 seconds to fire and the sound effect is that of an non-silenced gun.

After Matt picks up his car and is "driving" down the road and exploring his glove box, it is obvious that he is in front of a projection screen. The background shows his car going through curves, but Dean Martin never turns his steering wheel.

When Matt and Ironhead start fighting on the hovercraft, they are supposed to be alone but in the shots through the windshield, the pilot (in a white collared shirt) is clearly visible.

Wires visible just before Ironhead is ejected out of his moving vehicle.



Audio/visual unsynchronized

When Matt test-fires the silenced ten-second-delay gun, it goes off as loud as a non-silenced gun.