NTDS- Navy Tactical Data System

A brief history of the NTDS.

To say the Navy was an early adopter of radar would be an understatement. As of 1940, few if any US Navy ships had radar.


That’s a Benson class destroyer. That was the main model in production at the outbreak of the war. And yes, that’s a crows nest up top on the mast.


By the end of the war, this Fletcher class destroyer had an air search radar, a surface search radar, gunfire control radar on her main director, radar intercept receivers, and a jamming system, as well as at least one navigational homing beacon.

Virtually every combatant ship by 1943 had multiple radar systems, and most auxiliaries did as well. Airplanes had surface search and air intercept sets, submarines had search radars, and even periscope mounted ranging sets. Land based units of course had radars as well. Radar was everywhere the Navy went. Not an inch of the surface they sailed wasn’t assailed by trillions of electrons flung out in search of the foe.  And today’s reader may be surprised to learn that those sets were very effective. Their range and sensitivity over open ocean would compare quite well even with todays radar systems. Oh, there have been improvements, to be sure.  Greater power, greater reliability, and such. But the range of radar hasn’t really improved much since World War II. Physics sets those rules. Radar, for the most part, is a line of sight device. And since the earth is curved, a radar on at surface level has in inherent limit to its range. Toward the end of World War II, the Navy’s prime target was enemy aircraft, particularly the Kamikaze. The range at which a destroyer’s radar detected a Kamikaze was largely a function of the altitude a Kamikaze was flying at. Few Kamikaze raids at Okinawa went undetected. The relatively short detection range of a surface mounted radar against low flying raids led the Navy to station numbers of destroyers as early warning pickets further along the most likely avenues of enemy approach to give more warning time. The Navy was also developing airborne early warning radar systems to better detect low flying aircraft at longer ranges.

As valuable as radar was, it wasn’t without its limitations. Radar would tell a ship where an airplane was, in terms of range and bearing. But that information was of little use without knowing where the target was heading, and how fast. By manually plotting range, bearing and time information and using a little trigonometry and a maneuvering board, the radar operator could determine the targets course, speed, and best course for friendly fighters to intercept.  Against one or two piston powered airplanes, that was sufficient.  But plotting took significant time, and more than one or two targets overwhelmed the manpower available .

One way to avoiding this task saturation was to assign each escort a limited sector to plot, so more  fighter control teams were available to plot more interceptions. A master plot of  the total air picture was maintained on  the force flagship on a Plexiglas board. The pickets would  call in information via voice radio.   Don’t forget, every bit as important as tracking and plotting enemy air was tracking and plotting friendly aircraft. Only by continuously tracking every airborne contact could a task force be reasonably certain that every enemy raid would be intercepted or taken under anti-aircraft fire by escorts. Further, by plotting the location of friendly combat air patrols, fighter direction officers would know the best CAP to task to intercept a given raid.

But the Navy realized that with increased speeds of the jet age, the teams manually plotting air tracks would quickly become overwhelmed.  The engagement chain, from detection,  tracking, handing off to fire control radars, and developing a firing solution took time, time that the higher speeds of jets just didn’t allow.

Almost immediately after the end of WWII, a handful of radar specialists in the Navy began to search for a solution to the problem. They quickly realized any mechanical/analog computer system similar to those used in gunfire director/computer systems would be overwhelmingly complex. But a few had heard of the first forays into the electronic (digital) computer systems entering service such as the ENIAC. The plotting and tracking functions of any system of automation would largely be relatively simple mathematic calculations. The challenge wasn’t the complexity of the math, but the volume of it. And the ENIAC and its brethren were designed for the sole purpose of performing large numbers of mathematical computations.  The problem was, the ENIAC was as big as a house. The Navy’s codebreakers were also deeply interested in digital computers. Codebreaking is again an arena where the mathematical computations themselves aren’t terribly complex, but the sheer volume of calculations needed overwhelm both humans, and the primitive electromechanical devices used in World War II.

Working hand in hand with universities and private industry as well as pioneers in digital computing such as Seymour Cray, the Navy, over the course of several years (with Moore’s Law in effect) managed to procure digital computers that were little larger than a refrigerator. Massive effort also went into developing modulator/demodulator (modem) systems that would convert the analog input from radars and other sensors into the digital information a computer could process. Another massive hurdle was to develop displays for the operators. It wasn’t enough to simply show the raw radar picture. The system also had to generate symbology showing which targets were being tracked, and display the course/speed information the computer had divined on them (known as a “vector”). It also had to generate and display the interception vector computed for a friendly aircraft to intercept any hostile tracks. It quickly became apparent that even with computer support, one operator could only manage one or two interceptions concurrently. Accordingly, the system would have to provide multiple workstations for several operators, and accept input and generate output for each one separately. Finally, since the CAP was unlikely to defeat all possible raids, the system had to be able to cue and point fire control radars, gun and missile systems for close in engagements. Since these systems were analog, the computer had to go through another modem to convert its information back to an analog format that they could accept. Basically, the digital information would be converted to a DC electrical current that would vary, and drive a servomotor that energized the traverse and elevation drive motors of a fire control radar or gun mount. Once the track had been handed off, the fire control system would engage in its traditional (analog) manner, though the system still had to maintain its track information on the target until destruction.

Another major hurdle was sharing information. Even if a ship had sufficient computer power to quickly plot aerial targets, and provide vectors to intercept or cueing to fire control systems, unless that information could be shared across an entire task force (or at a minimum, across the with the fleet flagship and the primary anti-air platforms), there was still a very good chance that intruders could slip through. For instance, while each anti-air escort would still be responsible for its own “slice of the pie” sector, attacking aircraft were often inconsiderate enough to cross from one sector to another.  Handing off the track from one escort to another in the age of paper plots was time consuming, and without an automated system, the chance of overlooking a handoff was quite high.  In fleet air defense exercises in the early 1950s, as many as a quarter of all contacts were not tracked. And of the contacts tracked, as many as a quarter of those contacts were never assigned an interceptor or handed off to onboard weapons for engagement. Giving the enemy a free shot for almost half of its attacking force was simply unacceptable. Again, without an automated system to monitor all the contacts, the task force air defense could quickly be overwhelmed.

But how to share that plot information across multiple ships? Digital computing itself was in just the barest infancy. The idea of networking computers hadn’t even been considered.  Data had to be converted from raw radar return video to a digital format suitable for display on the operator’s scope. In addition, to be shared with other ships in the task force, accurate data regarding the source ships position, course and speed had to be injected. First, since contacts were referenced by their position relative to the reporting ship, to figure the contact’s true position, the receiving ship had to know the reporting ship’s position. Secondly, if two ships were both tracking the same target, knowing that positional data allowed the computer system to filter out duplicate tracks of the same target.

Given the wide dispersal of task force ships, long range High Frequency radio (HF) had to be used. That choice also meant a very low bandwidth for data. Smart communications people came up with an ingenious method to transmit information among NTDS equipped ships. A modified Radio Tele-Type would transmit (and receive, of course) information. Using a master/slave timesharing system (a simplex system, as opposed to a multiplex to you commo types) the master would query each NTDS ship in turn to update the shared air warfare picture.  Each ship in the network would listen in to each transmission. Having done so, all ships would have the same picture of all tracks in sensor range of the formation, even from distant radar pickets up to 400 miles away.

NTDS would grow in complexity as the capacity of computing power grew. Surface search radar and anti-submarine sonar inputs would be added, expanding NTDS from simply an air warfare tool, to a battle management system. Interfaces between NTDS and airborne early warning aircraft vastly extended the reach of sensors. Tying in the NTDS with similar shorebased systems for the Marines (the MTDS- Marine Tactical Data System) extended coverage over the shore).  Eventually the existing analog fire control systems would give way to digital systems, and be tied into the NTDS system. 

The NTDS system was expensive, and required considerable volume and personnel in a ship. Clearly it was only suitable for larger ships, generally those larger than a destroyer.  But in order to share the common sensor picture, a receive only system was developed to share information with smaller ships such as destroyers and frigates.1

NTDS quickly became the primary information superhighway of the Navy from the early 1960s through the mid-1990s. Any time the Navy needed to keep a clear picture of the air (and surface and subsurface) situation, off Vietnam, Lebanon, or off the shores of Iraq during Desert Storm, NTDS equipped ships were there.

Not until the boom in the use of smaller computers of the 1980s did the NTDS start to face obsolescence. Development of successor systems began in the mid 1980s, and by the mid 1990s, a variety of cheaper, faster, smaller and lighter systems began to replace it. Today several high bandwidth data links working in conjunction with advanced versions of the computer systems used in NTDS perform the battle management function.

In many ways, NTDS can be considered the earliest internet. Further, from a program management point of view, NTDS was also a first. Whereas the Air Force SAGE system used a computer that took up almost a half an acre, the NTDS performed virtually the same functions with between seven and 11 computers each  roughly the size of a refrigerator.  The NTDS was also the first program for which there WAS a program office. Rather than receiving input from the various bureaus and commands and cobbling together their consensus product, the program office received the input on desired functionality, but then held sole responsibility for defining, designing, procuring and supporting the product, with its own budget.

1. Known at that time as destroyer escorts, or ocean escorts. At the time of NTDS development, a “frigate” was a warship larger than a destroyer, but smaller than a cruiser.

Bibliographical note- I researched any number of sources on NTDS prior to beginning this post, but came across the motherlode (and in effect, sole primary source for this post) at IEEE with this excellent 9 part series of the development of NTDS. If you’re at all interested in the subject, or program management, or simply history, I highly recommend you read the whole thing.

8 thoughts on “NTDS- Navy Tactical Data System”

  1. When I was in NTDS was still pretty much a development project. A version was on the newer large ships, but much of the Destroyer were FRAMed WW2 Destroyers. The Dealey Class Destroyer Escorts were the oldest of that type in commission in the early 70s (Courtney was actually a few months older than I was). I think it had been retrofitted to the Fleet Flagships, which, on the whole, were fairly old ships. Albany (a WW2 heavy Cruiser that had Talos missiles fitted in place of the guns) was the 2nd Fleet flagship when I got out. ATDS (Air Tactical Data System) was still a twinkle in someone’s eye since computing power had not shrunk enough. As it was NTDS was also limited by computing speed, a problem that had been solved by the 80s. Now days speed is still a limit, but the capacity of such systems is enormous compared to 40 years ago when I was in (yeppers. It’s been that long ago now. Time flies when you’re having fun). NTDS was still something to talk about in casual conversation wishing you had it. About like the super sonars we were told were under development.

  2. Great read and a great find at that link…I can’t wait to dig through all of that.

    The first half of my career, before I went Narmy*, I was a cruiser and destroyer kind of guy, going down to the sea in ships. First ship was a non-NTDS destroyer (USS ROBISON), but I eventually moved up in the world to the USS LEAHY, an NTDS platform with the New Threat Upgrade. The modern Ticonderoga cruisers may be able to put more missiles in the air at one time, but the NTDS/NTU ships had them beat hands down on AAW range.

    One thing I wanted to mention, and perhaps it’s a distinction without a difference, or pedantry on my part from being an old LINK tech and having gotten my ESWS on these type of ships. First, the HF data system you describe as using a teletype is what we would have called LINK 14, a 75 baud HF system that took track data from NTDS and simplex transmitted it to non-NTDS ships, so they could manually plot the track data from our ship’s sensors. That interface between our automated NTDS/LINK systems and the LINK 14 circuit was a real pain in the ass for some reason. The more modern LINK 11 system is the automated NTDS-to-NTDS system…had a real smooth poll/response system that was great at sharing data on a low bandwidth commo link. On a humorous side note, since the HF radios we used were generally cranking more than 500W peak power, the LINK 11 audio bled all over everything…intercoms, PA systems, telephones, and the CCTV system. We got to where you could do some quick diagnostic guessing just be listening to the bleed over.

    I, and many other a Sailor, was sad to see the old ships go…in many ways they were superior to the AEGIS cruisers that followed, but with a thirty year old hull and a very expensive to operate set of 1200 psi boilers, the Navy just couldn’t afford them any more. I was part of the decommissioning crew for both LEAHY and ROBI.

    Thanks again for the post.

    * Narmy: Any of us poor Sailors who left the ship or aircraft portion of the Navy and worked the expeditionary or special warfare side of the street. Occasionally used to refer to Navy Individual Augmentees.

    1. Honest Injun, the IEEE describes the converted teletype as serving both Link 14 AND Link 11 purposes. Of course, NTDS evolved greatly over the course of a quarter century of service. The original processors were replaced fairly early on. In fact, the original original processors were replaced before they were ever used. Dig in. That’s a fantastic, if very long, article.

  3. Thanks for finally doing this one, Brad. I really enjoyed reading through that article. Took me quite a few days worth of lunch breaks at work …

  4. Ugh, xbrad, I think I hate you today. Thanks to your link to the IEEE “First Hand” account, I was up WAAAAY too late last night. Some great, and depressing reading.

    I’m amazed at what a small project office was able to accomplish in such a short time frame. Now, when compared against JTRS and other similar modern program offices, I feel very disappointed with our SYSCOMs.

    Seriously, though, thank you for this post and the link to the larger article. As one-time NTDS maintainer and operator, it was a fascinating look at how the system came to be as I knew it. The details were wonderful; the discussion of the AN/SRC-16 brought back a lot of great memories, as that was my primary maintenance responsibility as a junior Sailor. Oh, the stories I could tell about that behemoth.

    On the other side of the coin, I now support the Navy’s C4I SYSCOM so I was able to pick up some useful information, beyond the sense of disappointment, to hopefully improve my work here.

    Systems engineers and EDOs don’t run the Navy acquisition programs any longer, as the IEEE shows that they once did. Acquisition weenies run the show, and I think that may be the root of the difference between then and now. Capability delivery will take a back seat to regulatory/statutory compliance and milestone reporting. Sad, really, we deserve better.

  5. Thanks, ..this is all after my time..no data boy here, lol..just a mk 5 TDS with our mk 37..and 56 systems on a Gearing DDR..very interesting..my son was an ELT..and when the Texas pulled into North Island..I had a chance to go aboard..CG39..pretty cool..it was like a space ship for me though..lol

    1. I seem to recall we could receive a paint on our PPI scopes from aircraft in close proximity..sorry about the lack of memory..it’s only been over 50 years now, lol

  6. NTDS week link was that many ships had smaller ships. The reason behind this was their capability could only handle a limited number of tracks. In some cases other more developed had to limit the number of tracks that were put into the system. In some cases even modern ships need have to limit their tracking capability.

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