You might wonder why the US Navy SEALs would want a Scottish tartan. I do not have the answer to that question, although I did know a SEAL who was a prominent figure at the Grandfather Mountain Scottish Highland Games at one time.
In any case, a surprisingly large number of members of US military units have registered them in honor of their particular branch of service. The United States Marine Corps has the Leatherneck Tartan, which you can get in two quite different shades as you prefer. The US Army has a tartan, as do the US Special Forces, the US Army Rangers, and US Army Civil Affairs. The US Navy has a tartan as well. The US Air Force has one for the service, and one for its Reserve pipe band. Even the US Coast Guard has a tartan.
I'm probably even missing a few.
I guess a lot of Americans of Scottish heritage serve in the armed forces. In any case, though you rarely see a servicemember wearing a kilt outside of a Scottish Highland Games, it's more common than not for the option to exist.