I found a very interesting article about early fins, starting on page 25 of this PDF (written in 1994 By Dr Sam Miller who I actually contacted a few days ago about the Duck Feet). http://aquaticcommons.org/14990/1/Histo ... 3_1994.pdf
Dr Miller is extremely knowledgeable about the history of diving and super helpful.
These two iconic fins have been around for a very long time.
Owen Churchill started Churchill Fins in 1940 (the shape has changed little to this day) The US Navy purchased 50,000 pairs of them in 1943. These were the original UDT (underwater demolition team) fins.
Duck Feet were originally designed and manufactured by Art Brown in Laguna beach in 1950 by his company, The Spearfisherman Company. They made masks and fins. The Duck Feet fins at that time were all the length of current Duck Feet UDTs. Also very little has changed in the design since 1950 with the exception of the foot pocket and the shorter models you most commonly see today.