What Percent of Navy SEALs Are Marines?

A small percentage, estimated at less than 2 percent, of Navy SEALs are former Marines, since they are two different branches of the military. In order to become a Navy SEAL, candidates must be U.S. citizens, males between 18 and 28 years old, and in the Coast Guard or Navy.

It is not possible to become a Navy SEAL without first going through the Navy or Coast Guard. If a Navy SEAL was formerly a Marine, this means that he would have joined the Marines, dropped out, joined the Navy, and then applied to become a Navy SEAL, an unlikely but not entirely impossible career path in the military.