Sally port The primary modern meaning for sally port is a secure , controlled entryway , as of a fortification or a prison . The entrance is usually protected by some means , such as with a fixed wall blocking the door which must be circumvented before entering , but which prevents direct enemy fire from a distance . It may include the use of two doors such as with an airlock . In former times , from around 1600 to 1900 , a " sally port " was a sort of dock where boats would pick up a ship ' s crew and ferry them to the vessel anchored offshore , or vice versa . The term is occasionally still used today , especially in coastal Great Britain . However , there are not many old sally ports left . Etymology and historical usage . The word " port " is ultimately from Latin " porta " for door . Often the term postern is used synonym ously . It can also mean an underground tunnel , or passage ( i . e . a secret exit for those besieged ) . A sally , ultimately derived from Latin " salīre " ( to jump ) , or sortie , is a military maneuver , typically during a siege , made by a defending force to harass isolated or vulnerable attackers before retreating back behind their defenses . Sallies are a common way for besieged forces to reduce the strength and preparedness of a besieging army ; a sally port is therefore essentially a door in a castle or city wall that allows troops to make sallies without compromising the defensive strength of the fortification s . Targets for these raids included tools which could be captured and used by the defenders , labor - intensive works such as trenches and mines , and siege engines and siege towers . Sometimes enemy laborers were also targeted . Often , the besiegers ' beer and food supplies would be stolen or , if they were too bulky to transport , destroyed . Modern usage . Modern personnel sally ports are used to control entry into highly protected and restricted military areas , e . g . nuclear weapons storage areas , highly sensitive ( and large ) conventional weapons storage areas , e . g . small arms , munitions , etc . Sally ports are also used to control entry to highly valuable civilian facilities , such as currency or credit card manufacturing sites . A guard in a protected location ( today usually physically remote from the actual sally port ) will have control over the middle space between the two doors ; the operation of the doors of the sally port ; and the movement of all persons , materials and / or vehicles through the sally port . This sally port guard will have the means to check the personnel escorts and / or the credentials of all those persons , materials and vehicles to be passed into the protected space through the first opened door , prior to its opening . He will then monitor the sally transit to ensure that : Sally ports must be used with caution , and transit through them must be carefully monitored during any emergency or non - routine movements . The greatest safety hazard in use of these passageways is the danger of overcrowding the middle space between the doors . Since either door can only be opened while the other is closed and locked , overcrowding may occur in the middle space when too many persons , vehicles or materials attempt to enter it at once . Once the middle space is overcrowded , it may be impossible to properly close and lock the first door , thereby also making it impossible to open the second door , which of course is the only way by which people , vehicles or materials can successfully exit the controlled area . Even when the sally port has over - rides installed within the door controls and locking apparatus , the size of the middle space and the physical dimensions and layout of the door openings will act to hamper quick egress of a controlled space through a sally - port - type opening . Because of this danger , controlled spaces protected by sally ports usually have multiple sally port openings , safety zones within the controlled space ( for internal evacuation w / o leaving the controlled area ) , and formally written and routinely practiced procedures for the evacuation of persons , vehicles or materials . There is also continuous supervision and monitoring of the total number of persons , vehicles or materials within the controlled space to ensure that the designed evacuation maximum ( by whatever evacuation procedure ) is never exceeded . Sally ports are also used to restrict the flow of people to one at a time , so that intruders cannot pass into the classified or secure area on a cleared person ' s coattails . Military vehicular sally ports are similar to the personnel sally ports but have , of physical necessity , a large middle space to control the incoming / outgoing vehicle and personnel mounted in the vehicle . Mounted personnel are made to stand down , and the vehicles are inspected by guards . If the person or vehicle in the middle space is found to be unauthorized , the guard can " lock down " both gates , trapping the individual in question until a guard or police response force can neutralize and remove the person and / or vehicle . A sally port appears on the Coat of Arms of the Republic of Malta In modern court buildings , a sally port secures the prisoners in a holding area or brings them directly from the jail area separating them from the court , with entry through the sally port controlled by the bailiff . In " supermax " correctional facilities , groups of inmate cells may be connected to central corridors via sally ports . An officer behind protective glass opens the port doors individually after verifying that the person is allowed to pass . Police departments may have an enclosed garage or other access point at a private door leading to their building , so that an arrested person cannot escape during transfer from a patrol car and a holding cell .