UDT stands for Underwater Demolition Team. These are the fins used by the frogmen of the 50s and 60s who preceded the Navy SEALS. UDT fins were state of the art in their day, and although the Navy has since upgraded their technology, the original UTDs remain a coveted piece of kit for bodysurfers and divers in the civilian world. I recently picked up a pair of my own.




In World War II, the Allies achieved victory through a series of beach landings in France, Italy, and the Pacific Islands. These landings were made possible, in part, by a small unit of frogmen who swam ashore ahead of the invasion to scout the beachheads and clear obstacles with explosives. They were armed with K-Bar knives and dynamite. Their losses on D-Day are estimated at 50%


The frogmen of WWII wore short rubber fins, similar to those worn by bodyboarders today. A  statue of a frogman at the Navy SEAL Museum, dubbed ‘the Naked Warrior,’ holds a pair of these fins.


After the war, the Navy developed the UDT fin for their elite divers. These were more powerful and better suited for use with SCUBA, which had just been invented. Around this time, surplus fins and civilian replicas became popular with bodysurfers in southern California. Legend has it that when the Navy discontinued UDT fins in favor of the Aqualung Rocket, an Orange County bodysurfer by the name of Dr. Greg Deets got his hands on the original molds and started making them himself.



UDTs are either loved or hated by bodysurfers. You could say that the entire evolution of swim fin technology over the past 50 years has been an effort to develop something lighter, more practical, and easier on the legs. But for those who swear by them, UDTs offer Poseidon-like power that more ergonomic designs simply can’t match. These are a must for big-wave riders.



I unboxed mine at Windansea (above) and jumped right in. El Niño was pushing a swell of decent size, not the conditions I would have chosen to try out new gear. Immediately, I had to adjust my kick for the added length of blade. The weight on my feet gave me plenty of downward momentum when I put my toes to the sky to duck-dive.

When it comes to catching waves, there’s a lag between the time you start kicking and when the fins engage, but once you get moving you can catch anything.

UDTs are now my go-to in the big stuff. But their length makes pushing off the bottom into fun-sized shore-break a little awkward. If you’re an occasional bodysurfer or live somewhere with modest swell, I’d go with a pair of DaFins or Vipers.



On a recent trip to Ireland, I wore them snorkeling. They were great for cruising along the surface, but when I dove to about ten meters, it became clear that fins have come a long way since the Truman administration. Much of the power the UDTs deliver comes from their stiffness, but that power comes at a price. Kicking with a stiff fin is exhausting and taxes your oxygen supply. Modern free diving fins have largely solved this problem and the new records in that sport speak for themselves.

An alternative to the latest gear is modifying the old stuff. Some divers customize their UDTs for free diving and spearfishing. They sand down the thick rails that give the fins their stiffness or cut the blades into a ‘V’ shape. The DIY approach is not only an act of recycling but a tribute to the legacy of the frogmen who earned their reputation by making do.

Voit UDTs retail for $60. I picked up mine at Mitch’s Surf Shop in La Jolla, California. You can also find them at Sea Craft Supply Co.

Images: Navy SEAL Museum,  SaeahLee Photography