The U.S. Navy Sea-Air-Land (SEAL) program grew out of Navy Underwater Demolition Team (UDT) experience in World War II. SEALs began as a secret military program in the 1960s, first created by President John F. Kennedy. The first set of trainers and commanders, old UDT frogmen, still remembered experiences of sharks picking off UDT members in and around Pacific Ocean islands in World War II. The great loss of men experienced by the sunk carrier U.S.S. Indianapolis due to shark attacks was very much on the minds of early UDT instructors.
The U.S. Navy SEALs are expert swimmers. They train in high surf, bad weather, and cold water. Sharks are just another problem to overcome.
Some SEALs hate sharks with a passion. One such SEAL, Scott Slaughter, was described in a book on early SEAL team members (a book that I unfortunately gave away). If he worked or trained in waters with sharks, he would free dive 100 feet down with a bang stick and kill sharks just for fun. A bang stick is a long stick with a quarter stick of dynamite at the tip, that could be set off by sharply striking a shark. The percussive force would kill even fairly large sharks. He'd dive, find a shark, kill it, drag it to the surface, and boil it down for its jaws, which he kept as a trophy. One less shark in the water.