The strip seemed too fantastic to ever happen outside of a comic, but now it's a reality! The Seabreacher is a range of submersibles that look and perform very much like the craft in the comics. I'm sure it's just a coincidence, as they both use a fish design as a template, but it's still a thrill to see an "Iron Fish" in the real world.
You can find out more about this amazing craft at the Seabreacher website here:
Here's a classic Iron Fish episode drawn by Albert Holroyd for The Beano No.1126, February 15th 1964...
My thanks to Stephen D. Quirke for bringing the Seabreacher to my attention.