To communicate the order, the CJCS, or, in his absence, the senior officer in the NMCC verifies the President's identity with a "challenge code" and the President responds with the corresponding authentication code from the biscuit. Additionally, the message will go to the Alternate National Military Command Center (ANMCC), located in Raven Rock Mountain, Pennsylvania, and also to an airborne command post, either the presidential National Airborne Operations Center (NAOC) or the military E-6 Mercury Looking Glass. If the NMCC is destroyed by a first strike, either the ANMCC, NAOC or Looking Glass can issue the orders to execute the SIOP.