Air Force pursuing antimatter weapons Program was touted publicly, then came official gag order San Francisco Chronicle

The U.S. Air Force is quietly spending millions of dollars investigating ways to use a radical power source — antimatter, the eerie “mirror” of ordinary matter — in future weapons. The most powerful potential energy source presently thought to be available to humanity, antimatter is a term normally heard in science-fiction films and TV shows. But antimatter itself isn’t fiction; it actually exists and has been intensively studied by physicists since the 1930s. In a sense, matter and antimatter are the yin and yang of reality: Every type of subatomic particle has its antimatter counterpart. But when matter and antimatter collide, they annihilate each other in an immense burst of energy.