book listing a menu of strike options and "The Biscuit," a 3-by-5-inch card with authentication codes for the president to confirm his identity. The menu of strike options include Major Attack Options (MAOs), Selected Attack Options (SAOs), and Limited Attack Options (LAOs). Individual countries or regions can be included in or withheld from nuclear attacks depending on circumstances. 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. The senior NMCC officer directs preparation of the launch order in the form of an Emergency War Order (EWO) – a message that contains the chosen war plan, time to launch, authentication codes and codes needed to unlock the missiles before firing them. A second officer will validate that order. The order is then broadcast to each worldwide command and directly to launch crews by releasing an Emergency Action Message (EAM) which is an encoded and encrypted message about 150 characters long. As the orders go down the chain of command, always subject to the two-man rule, intermediate headquarters, and eventually the nuclear delivery platforms themselves, will receive Emergency Action Messages (EAM) to arm or launch weapons. For most modern weapons, the EAM will also include codes for Permissive Action Links (PAL). At a minimum, a PAL code will actually arm a weapon for release. The circuitry controlling the PAL is deliberately positioned inside the warhead such that it cannot be reached without disabling the weapon, at a minimum, to a level that would require a full factory-level rebuild. There may be separate PAL codes for arming and launch. Some weapons have "dial-a-yield" functions that allow the power of the nuclear explosion to be adjusted from minimum to maximum yield. Most weapons have additional arming circuitry that, even if a valid launch code is entered, will not arm the warhead unless the weapon senses that it has been released on an