Admiral William McRaven, the head of the military's secretive U.S. Special Operations Command, is a former Navy SEAL who oversaw the elite forces that hunted down thousands of Iraqi militants during the worst years of the war and personally ran the 2011 raid that killed Osama bin Laden.
He's not, in short, a man known for being soft and cuddly. Recently, though, McRaven was asked to take on a very different kind of mission: settling, once and for all, the difficult question of how SEALs measure up to ninjas.
"Dear Admiral McRaven," the handwritten letter from 6-year-old Walker Greentree began. "When I grow up I want to be a SEAL too, but can you tell me who is quieter -- SEALs or Ninjas? Also, how long can you hold your breath for?"
McRaven, despite his well-deserved image as a tough guy, wrote back.
"I think ninjas are probably quieter than SEALs, but we are better swimmers, and also better with guns and blowing things up," McRaven wrote. "I can hold my breath for a long time, but I try not to unless I really have to."
McRaven sent Greentree a coin emblazoned with his personal symbol, an eagle holding a trident, and ended his letter with a bit of career advice.
"Remember, if you want to be a SEAL, you must do two things: listen to your parents and be nice to the other kids," he wrote. "If you do that then you can probably be a SEAL too."
Walker's mother Vivian, who runs a support organization for military families, says McRaven's letter won over her son.
"He definitely wants to be a SEAL now," she wrote over email. "He wants to carry a trident."