In January, a group of high-level military commanders gathered at an air base in Yemen. It was far from the frontlines of the country's ongoing civil war.
Then, without warning, a small drone appeared out of the sky and exploded, spraying the group with shrapnel. According to news reports, the blast killed several, including the Yemeni government's head of military intelligence.
Listen to Nicholas Heras' full conversation on NPR's All Things Considered.