According to the Producers Creative Partnership Mediterranean Film studios website, (http://www.the-pcp.com/a-short-history-of-maltas-water-facility.html) the very first natural horizon tank built at the Malta facility was constructed for the production of the miniature effects for this film by Special Effects supervisor Benjamin “Jim” Hole in 1963.
James B Harris who was Stanley Kubrick’s Producer for some of his early output, directs a really tight story of Cold war tensions escalated to dangerous levels and filmed in gritty black and white. The miniature work is uniformly excellent and totally uncredited. There is a brief reference to a model making company called Shawcroft models having worked on the film here; http://www.richingspark.com/newhistory/shawcroft.html
The miniature of the title, the USS Bedford, is a Farragut class destroyer and is well detailed and realistically weathered. The motion through the water is very well done with a nice slicing bow wave and swinging by the stern turns. There is a Russian submarine in the story but all you see is a periscope and snorkel protruding above the surface. In some of the frame grabs you can see the difference in water texture between the overflow edge of the tank and the much more distant real ocean horizon though I never noticed this viewing the film as it really is a compelling story very well crafted by all involved.