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.
In the discotheque scene, one of the band members (Dino) is Dean Paul Martin, the real life son of Dean Martin. Another (Desi) is Desi Arnaz Jr.. They had a one-hit wonder band at the time called Dino, Desi & Billy.