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Switched defense telephone network
AUTOVON (Automatic Voice Network) was a military
telephone system that was
developed in the US in 1963 to survive nuclear attacks.
It allowed non-secure voice calls with precedence (piority override).
In the late 1960s, the DoD started the roll-out of a secure version
of AUTOVON, called AUTOSEVOCOM, but this project was cancelled
a few years later due to problems and high cost.
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Both systems were later replaced by
IVSN (Initial Voice Switched Network), developed in the mid-1970s by
NATO for unclassified voice calls.
It was intended as replacement for the expensive AUTOSEVOCOM system.
Starting with 4 switches in Europe in 1980, the system grew to 24 switches
at the peak of its use in the mid-1980s.
The blue telephone set shown in the image on the right was
used with this network. It has an extra column of (red) buttons on the keypad,
which is typical for AUTOVON and IVSN phones.
The red buttons were used for priority override.
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Also typical for this desktop set, is the black push-button on the handset
— used as push-to-talk (PTT) in half-duplex conversations — and an indicator
lamp close to the cradle.
The IVSN network was operational for more than 25 years.
When it was officially closed down on 30 November 2005 it still consisted
of 18 switches, some of which were still in use in 2011 [1].
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IVSN had four levels of priority override:
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FO Flash override F Flash I Immediate P Priority
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The four extra keys generate DTMF-signals in the rarely used
1633Hz column. On some later keyboards, these keys are sometimes called
A, B, C and D.
After a nuclear attack, it would be very difficult for government officials
to obtain a free telephone line, as nearly everyone would try to make a
phone call.
By pressing the letter P, the user would signal the switch
to assign a free line by priority. Higher ranking officials were allowed
to press I (Immediate) to get a higher priority.
Military users were allowed to press F (Flash) in order to get a free
line nearly instantly.
It was thought that only the president and his circle were allowed to
use FO (Flash Override) to give them the highest possible priority.
Note that not all levels of priority override were available to
all subscribers; the required priority level
had to be assigned to specific nodes first.
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AUTOVON and IVNS networks did not provide encryption,
but were able to carry calls that were placed via (NATO approved) crypto phones
that were connected to the network. In some cases the call had to be initiated
in-clear, after which one of the parties decided to go secure.
The following crypto telephones are known to offer support for AUTOVON and
IVSN networks:
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Any links shown in red are currently unavailable.
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© Crypto Museum. Created: Saturday 21 October 2017. Last changed: Tuesday, 02 May 2023 - 19:43 CET.
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