AUTODIN (Automatic Digital Network)
by Jared Hall

The AUTODIN was originally developed in the mid-1960s and provided Message Switching functions for the US military. AUTODIN handled military record communications and communications support for special intelligence communities. AUTODIN outlived it's expected service life and was ultimately replaced with the MilNet Packet Switching network (The "original" components of the Internet) through the early 1990's.

AUTODIN was an interesting network. Most end-users interconnected to the AUTODIN through Digital Subscriber Terminal Equipment (DSTE) terminals. These used a modified version of the synchronous, byte-oriented, IBM Bisync protocol. Subscribers could also interconnect via asynchronous terminals, the most popular being the good ole' "Mode 5" teletype terminal. Although only a teletype, these systems could also employ circuit-switching techniques, establishing a direct link to the receiving device (ex. Telex). AUTODIN was maintained by the US military and Western Union in the United States and maintained by Ford Aerospace and the US military overseas. At the time, overall responsibility for AUTODIN lay with the Department Of Defense's Defense Communications Agency (DCA).

How It Worked

Generally, if one had a data communications requirement, they would approach their local planning department or projects office (XO). After all of the justifications, resource identification, etc., the project is finally funded and orders are placed for equipment and interconnecting circuits. Equipment orders went up the standard procurement chain. In the US, a special group called DECCO (Defense Commercial Communications Office) in Ft. Huachucha, AZ managed all the AUTODIN interconnect circuits.

Eventually, you'd get a call that a crew would be out at some scheduled time to install the equipment. These would normally be special install crews from the appropriate military branch. The AUTODIN switches would be programmed and Western Union would coordinate the installation of the line with the AUTODIN switch Technical Control personnel. Most installations were connected to the nearest AUTODIN switching center, in the interest of reducing costs.

Using AUTODIN was pretty simple. Whether you're using a teletype or a glass tube connected to a synchronous circuit using ASCII, the process is identical. First, you bang out some header information. This includes things like; (1) who you want to send to, (2) who you are, (3) a priority statement, (4) maybe a security classification, (5) and a subject line. Now, you type out your message. Then, you run your tape through a tape reader or hit the enter key on your glass tube. That's all there was to it In some cases, you could even type out your message on a standard piece of paper and run it through an OCR.

The AUTODIN switch accepts your message and sanity checks it. If it all looks OK, it is then placed in a buffer where it is sorted and queued up for transmission over a trunk circuit to the recipient's serving AUTODIN switch. Many operations only had daytime hours, and thus provisions were made to store their data outside their normal business hours.

The serving AUTODIN switch accepts the relayed message, and sends it to the proper circuit. At the recipient's location, the message is usually printed out by a Computer Operator and deposited in a mailbox. Alternatively, it might be displayed on your glass tube or your local printer.

AUTODIN Site Personnel

Most US AUTODIN switches only had manning requirements of about 60 military personnel. There would be about 10 Front Office personnel, maybe 15 Technical Controllers, 10 Crypto technicians, and 20 Computer Operators. Western Union probably had about 30 people at each site; including shift-working technicians, a site chief, and some administrative and Engineering staff.

All sites had some type of backup power available to them. Immediate power load could be assumed by large MGs (Motor Generators), while backup diesel generators were cranked up. This would be tested periodically just to make sure that the bleary-eyed military Power techs could bring up the generators before the MGs ran out of juice. The Power guys rarely would (or could) enter the building, so you never saw 'em.

Front-office personnel always consisted of at least two military officers: the site chief, and the Special Security Officer. Technical Control usually had three NCOs in the office, overseeing Management, Training, and Circuit Actions duties. Operations had a similar complement of front-office people. Things were normally laid-back. AUTODIN sites were inherently isolated from most other base functions because of the security constraints.

Every once in a while, we'd get one of these "gung-ho" First Lieutenants on-board. What happens when a light-weight, high-velocity mass (Lieutenant) meets an object of enormous mass and little speed (Western Union)? The light-weight mass loses velocity. So to its credit, Western Union was able induce rapid attitude change in these individuals.

The Crypto techs had their own special room in the AUTODIN facilities. The Tech Controllers and Western Union would normally use an intercom to communicate with the Crypto people. The crypto vault at Gentille came equipped with a futon and an alarm clock. Every once in a while a Controller would have to go back there and wake up a sleeping tech.

Operations had the largest amount of space. They oversaw most of the computer activities that went on and coordinated frequently with Western Union. They also handled most of the incoming calls from the end-users. The Console Operators would check all the computer stuff out. If it checked out OK, they would use an intercom to have a Tech Controller look at the problem. If problems were related to local computer systems, Operations would normally use an intercom to contact Western Union directly.

The Tech Controllers and Western Union shift workers shared the same area. Generally, calls would come in via intercom from Operations. They normally provided a "Jack Number", which made it easy for the Tech Controllers to "punch up a circuit" on an oscilloscope. However, the Tech Controllers also got calls directly from other Tech Control facilities, Western Union, and from Job Control or Operations centers at the larger military bases.

Life in Technical Control

The Technical Controllers were responsible pin-pointing defective equipment in a circuit path. As calls would come in, the first order of business was to properly translate internal "jack numbers" with Circuit IDs. Of course, there were always errors. I also observed that Western Union also had the same chaos - just more organized and structured!

When calls came in, the first order of business was to look the the "red" (clear-text) side of the circuit. Most problems just required a resynchronization of the crypto equipment, especially those old, or "cheapo" customers that couldn't install automatic resync gear. Line-related problems could be diagnosed by looking at the "black" (encrypted) side of the circuit. Of course, there were patch panels that facilitated loopbacks and external test sets.

In most cases, line problems were simply turned over to Western Union for resolution. In the event of trunk circuit failures (circuits that interconnected the AUTODIN switches), the Technical Control facilities had special 4-wire AUTOVON dial-up circuits through which to restore communications. Use and testing of these facilities occurred between the Technical Controllers and AT&T. AT&T had much more automated test equipment than we did. During quality control checks, they would sometimes get frustrated while waiting for us to swap in and configure test equipment manually. If the backup circuits were flaky, AT&T was real good about tracing the calls and rerouting calls over better paths.

Working With Western Union

I truly enjoyed working with the Western Union technicians. They ran the full gamut - from the slim, techno-whizes to the butt set-carrying/crack-showing, cigar-chewing, pant-splitters. There was even one crazy engineer who could tell 20 mA current loop circuits from 60 mA current loop circuits by sensing the current flow through his body. (Don't try this at home...volts do factor into the equation)! Still, for ambitious Technical Controllers, Western Union offered plenty of raw data-communications experience from which to learn.

Western Union taught me to respect other people's information. How easy it is to forget that any error can ruin someone else's day. In today's world, its far to easy for a System Administrator to blow away errant-files, without even thinking about ownership or the impact to some unsuspecting individual in the network.

Western Union taught me to respect other Tech Controllers time by checking out everything in-house first. This is a lesson that I still have to relearn from time to time.

Western Union also showed me that no matter how much technology is put into a process, things can still go awry. One case in point: high-tech Western Union microwave versus Mother Nature's temperature inversions.


A newer system was planned to replace AUTODIN. Called AUTODIN 2, this network was packet-based, with trunk circuits employing ADCCP (Advanced Data Communications Control Protocol) at Layer 2. Testing of the new network was started in 1981 at a few of the US AUTODIN Switching Centers. Unique to the network was a cluster of 3 PDP-11/70s that did most of the central processing. Two of the three PDP-11/70s were always online, while the third PDP-11/70 functioned as a "hot standby". The PDP-11/70s operated over Ethernet, a "new" technology at the time. Training was supplied by Xerox PARC.

In the end, an Ethernet failure caused by a defective coax cable halted any further testing or deployment plans for AUTODIN 2. ADCCP went by the wayside, yielding to the ITU's LAP-B (Link Access Procedure - Balanced). The PDP-11/70s were shuffled around the AUTODIN Switching Centers and redeployed to support Automated Patch and Test Facilities.

AUTODIN has been replaced by the Defence Management System (DMS) and became operational on Sept 15, 2000 thus becoming the military's official system for passing all general service messages
classified at the top-secret level and below.  It also modernized command and control messaging capability by allowing for multimedia attachments. DMS was implimented on more than 360,000
desktop computers at more than 7,000 sites worldwide in 2000.


1) Web page of Jared Hall

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Oct 14/05