Basic Underwater Demolition/SEAL training was divided up into four parts. Indoc, first phase “conditioning,” second phase “diving,” and third phase “land warfare” which the last weeks were spent on a shark-infested island over 80 miles off the coast of California called San Clemente. 

The brutal training was modeled after the original Underwater Demolition Teams (UDT) from World War II. The UDT teams were legendary for swimming ashore at night, armed with masks, fins, a knife, and some explosives. They would scout beach landing sites, map the beach depth, and sometimes if required, conduct demolition work. All this allowed the Marines to land their landing craft the next morning. 

The song went something like this:

“Marines will say they’re first ashore but UDT was there before.”