the state of having been made ready or prepared for use or action (especially military action)

engaged in or accustomed to close observation

warn or arouse to a sense of danger or call to a state of preparedness

the condition in which combat aircraft are airborne and ready for an operation

the highest level of alert when an attack by the enemy seems imminent (or more generally a state of alert resulting from imminent danger)

a state of readiness for domestic defense aircraft