The whole picture on Frogman! is pure fantasy anyway. The artist was probably some staff artist for Penguin Books who knew very little about diving. The fact that the book takes place in WW2 shows that.
No frogmen used aqualungs at that time; the only ones in existence were in Nazi occupied France.
The actual book has the frogmen using rebreathers, which is correct. The artist I'm sure didn't read it, and since this paperback was for the US market, he put an American frogman on the cover. The dynamite is pretty hysterical though; how was he going to light it? Obviously a waterproof fuse, and he was going to use an underwater flare to ignite it..
And his Aqualung hoses were obviously weighted to keep them from rising up..
Which would be needed, as the frogman has no weight belt that I can see..
It's still a great picture, and a good example of the love affair the public had with scuba diving during the Sea Hunt era...