Signal is clearly not a safe place to be discussing military operations, yet nor are its rivals Signal is the fashionable place to discuss shady business – and that is probably what tempted National Security Advisor Mike Waltz, a military man with a previous in at the Pentagon, into using the app to discuss American air strikes against the Yemeni Houthis with top Trump administration officials. It was Waltz who added the Atlantic’s editor-in-chief Jeffrey Goldberg to the “Houthis PC small group”