I remember reading that article. I think the best sub got to 8 MPH. More into human powered aircraft at the time, gossamer Condor (in the smithsonian) Albatross (flew the English channel) and Penguin (which flew the mythical Daedalus-Icarus route). The Penguin was good enough to actually get some altitude and pulse and glide, giving the pilot a chance for a brief rest.
Edit;
I might be wrong on the Penguin, apparently it was solar powered.
Gossamer Condor - Wikipedia, the free encyclopedia
Gossamer Albatross - Wikipedia, the free encyclopedia
Gossamer Penguin - Wikipedia, the free encyclopedia
regards
Mech