Just seen a video of it being tested in a swimming pool, I assume an early version.
In that form it would not have worked. Why, too inflexible, the children were I understand about 11 to 17 year olds so it maybe would not have “fitted all”.
How many extra divers and supplies would have been required to lift the sub over dry sections on the way out.
No a tried and tested system was used.
Could this sub have been just a publicity stunt ? I hope not !