Listen carefully. A Seal can use any knife he wants, but the Seals hold competitions periodically to determine the best knife for their needs.
Kevin MAD DOG McClung won one such competition with his ATAK, a knife that retails for close to a thousand bucks. Here's a picture of one of his many fine knives, although not the ATAK.
http://img.villagephotos.com/p/2003-...arlockPic1.jpg
When I tell you something about a knife, believe it.