The vehicle had long been known from the pages of TV 21, where it featured in a Ron Embleton illustrated Stingray strip, which presumably was based on the actual toy.
You can read about some of the history of the toy and speculation about the box art here:
https://projectswordtoys.blogspot.com/2022/06/david-nightengale-and-submarine.html
However, I was researching an entirely different vehicle yesterday and came upon an interesting site called Air Force Declassification Office https://www.secretsdeclassified.af.mil/ which at first seemed to be a unauthorised site showing patents and documents released by the military under freedom of information auspices.
There isn't a great deal of information on it, but as a document relating to the launch of a Cold War 'Sputnik' satellite caught my eye, I was drawn in. Shortly after, I saw another interesting read, about Submersible Aircraft. The document by Rand Corporation, from 1964, was a proposal for aircraft which could be stored and launched from a submersible base, thereby extending the range of a penetrator or bomber aircraft. The document shows the various wing and engine geometries ad also shows images of proposed nuclear carrier vehicles, which all bear a striking resemblance to the toy!
The full pdf can be viewed here: http://tinyurl.com/5bwf9v4t
Below are some highlighted images from the document.