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Editor’s Note: Lieutenant Nisbett’s paper won The Naval Submarine League Essay Contest for Submarine Officers’ Advanced Class 99020. Lieutenant Nisbett is currently the Weapons Officer on USS OLYMPIA (SSN 717).

From June to December 1998, I had the opportunity to deploy with the Eisenhower Battle Group as the Submarine Operations Officer on the Destroyer Squadron Thro staff. During the deployment, DESRON Thro participated in six different multinational Undersea Warfare (USW) exercises in which a total of nine diesel submarines and. five U.S. fast attack submarines participated. 1he Battle Group had Tactical Command (TACOM) of four SSNs simultaneously. I had the unique opportunity to participate in all the planning and execution of the USW exercises. As a submarine officer, my previous USW experience was limited to the single dimension of hunting below the surface of the ocean. I gained many valuable insights while on the staff as to the very complex three dimensional problem of USW which incorporates air, surface, and submerged assets to hunt for enemy submarines. One particular high tech, USW non-acoustic sensor captured my attention, and this article attempts to explain this USW sensor and its implications on future submarine employment and tactics. The article will also explore the impact of similar, high tech, commercial-off-the-shelf (COTS) technology in the Virginia class submarines, as well as technology that is being back-fitted on Los Angeles class submarines.

Those in the submarine profession fully understand the term of acoustic advantage, and they understand the significance of the declining acoustic advantage as Russia continues to produce highly capable and stealthy submarines. Acoustics aside, there is no such term that refers to the submarine’s radar stealth advantage in approaching and attacking a surface ship, however, decreasing the radar stealth advantage of a submarine has implications equally serious to the decreasing acoustic advantage. The surface ship’s ability to detect a submarine mast with its surface search radars has yet to pose a significant threat. A submarine can approach a surface ship using short mast exposure times and only reveal its presence when the submarine’s torpedo explodes and the ship is on its way to the bottom of the ocean. It is a challenge to the submarine’s way of thinking to imagine a world in which a surface search radar can detect a submarine’s periscope and vector a helicopter to prosecute before the submarine can visually detect the surface ship.

Automatic Radar Periscope Detection nod Discrimination

Such a radar system exists today, and it is known as Automatic Radar Periscope Detection and Discrimination (ARPDD). The incredible digital storage capacity and lightning fast processor speed of commercially available computer hardware enables the radar system to track all initial detection’s, including wave clutter (up to 100 detects/second), and track each detection to develop a course and speed. A complex three layer algorithm is performed on each detection which effectively analyzes the sea state to filter out the clutter returns, it analyzes the shape and the stability of the object in the water, and then automatically provides the operator with a valid periscope declaration. All this with only brief moments of mast exposure! The operator is spared the overwhelming returns from wave clutter and trash in the water and is only given the real periscope return. The operator then has the tools to further analyze the information for the aspect of human evaluation.

ARPDD utilizes the AN/APS-137 ISAR radar mounted on S-3 and some P-3C aircraft. The AN/APS-137 was originally designed as a periscope detection radar with two modes, search mode and searchlight mode. In search mode, the operator was presented with all radar returns, whether the returns were trash, sea state, or a periscope. The operator would then switch to searchlight mode in order to evaluate and discriminate the returns. Search lighting was immediately detected by the submarine’s ESM system causing the submarine to lower its periscope or to proceed deep. Unless in an alerted condition, the APS-137 operator might miss the mast detection. ARPDD utilizes modern digital technology to replace the human operator functions of identification and discrimination of a short exposure periscope detection. The radar characteristics are unchanged, and the requirement to use the searchlight mode is available but no longer necessary. By installing the APS-137 on a surface warship, the warship is provided with a non-acoustic, USW sensor that will detect a submarine periscope beyond the visual range that the submarine can view the warship.

ARPDD offers promising benefits in the war against the diesel submarine. Passive sonar is generally ineffective against a diesel submarine. Active sonar produces better results, but it is highly unlikely that the environment will support the use of active sonar, and counter-detection is a great disadvantage of active sonar. Mountains of evidence have been collected that prove non-acoustic sensors provide the majority of detection against diesel submarines, the primary sensor being the human eye of a pilot in a helicopter or a fixed wing aircraft. By nature of their design, diesel submarines must spend a large portion of time at periscope depth in order to snorkel. The correlation is clear between the amount of time diesel submarines spend at periscope depth and the number of detection of diesel submarines by visual detection. Armed with ARPDD, ships have a force multiplier that is many times better than human vision. ARPDD provides the operator with automatic detections, requiring only brief periods of mast exposure, well beyond visual range of a lookout and with highly reliable, 24-hour coverage.

ARPDD was to be tested in the P-3C aircraft during 1999. The mobility added by the MPA aircraft will further its usefulness in locating diesel submarines. ARPDD also has great potential as a coastal defense radar. ARPDD could be affordably used to prevent submarines from collecting information off the coast or to prevent special operation forces from invading a beach head. The potential is very high, and the remarkable factor is it only takes a modem radar with the right operational attributes in bandwidth, range resolution and update rate (the ISAR radar) along with COTS computer hardware to create such a system.

In the Falklands War, hundreds of British USW weapons were employed against Argentine submarines without success. To prevent this large expenditure of weapons against false contact, the U.S. adopted a more conservative doctrine of weapon employment. Three types of submarine detection were defined: Possible Sub, Probable Sub, and Certified Sub. The only way to classify a submarine as a Certified Sub according to the doctrine is to visually identify the sub. The ARPDD system proved to be so reliable during its first deployment that a detection was definitely a submarine, but according to the doctrine it could only be reported as a Possible Sub or Probable Sub. The system was so much better than the traditional sonar detection, either by surface ship bow mounted or towed array sonar or aircraft dropped sonobuoys, that it did not fit in the USW doctrine. This is only the tip of the doctrine iceberg that must be evaluated and changed to incorporate the far reaching effects of computer technology.

Submarine SUW Tactics and Equipment−The Present and the future

ARPDD is a highly capable radar system that surpasses any periscope detection radar available today, but it does not make the submarine obsolete. The capabilities and limitations of the ARPDD system makes clear that the nuclear submarines will remain the submarine of choice due to factors of speed, maneuverability, survivability, the ability to remain submerged, continued sustainability, communications, and rapid firepower of multiple weapons that only nuclear submarines can guarantee in any situation. However, the U.S. Submarine Force must always focus on the future to continually evaluate what systems may pose a threat and then invest the resources to counter that threat, whether it be with tactics or technology. The submarine community must be on the leading edge of research and development to maximize not only the acoustic advantage but every advantage that makes the submarine such a lethal, stealthy, and highly versatile platform.

The impact of such a radar system on submarine tactics is significant. ARPDD effectively removes the submarine’s ability to identify and distinguish surface targets visually. The risk of counter-detection for the submarine increases dramatically. The extended range of ARPDD on a surface ship is about 20 kyds, which is limited by the horizon and the mast head height of the surface ship. The submarine’s only defenses are Sonar and Electronic Support Measures (ESM). At 20 kyds, a warship could detect a submarine at periscope depth well beyond the submarine’s sonar range. ESM is limited as well by the short mast exposure time. By the time the ESM operator reported a signal strength 2 or 3 threat contact and the 000 lowered the periscope, the necessary time for counter-detection by ARPDD would certainly have elapsed from the moment the periscope initially broke the water to the time it was subsequently under water. In that short amount of time, the ·submarine was counter-detected and in moments will be prosecuted by helicopters or fixed wing Maritime Patrol Aircraft (MPA).

How does the submarine participate in Surface Warfare (SUW) in an environment in which every surface combatant has an ARPDD radar? The scenarios of unrestricted submarine warfare practice during World War I and II offer the only legitimate case when submarines would have the freedom to sink surface vessels without discrimination. Such indiscrimination would be unthinkable in today’s political environment. In fact, blue-on-blue engagements and blue-on-neutral engagements are key items of concern during inspections of deploying battle groups. By denying the submarine the ability to penetrate within visual range of a warship, the submarine is either forced into an Over the Horizon engagement or the submarine must be willing to sacrifice its stealth during the attack.

In order to conduct a surface attack using torpedoes, the submarine can easily penetrate the surface defenses to within weapon range while submerged using sonar. It is recognized that against a capable adversary, the submarine sacrifices its stealth once the torpedo is deployed. The submarine must recognize that it can no longer make a round of observations while approaching a surface ship equipped with ARP DD. It must make the approach submerged, the firing TMA solution must be obtained submerged with the firing tactics assigned, and the torpedo must be ready to fire with the tube flooded and the outer door opened. The captain, as the approach officer, can make one observation of the surface ship for identification purposes only to verify the contact is classified correctly and to ensure there are no interfering contacts. Odds are that the submarine will be counter-detected by ARPDD once the scope is raised, but against the capable adversary this equates to only a few seconds difference from when the torpedo is fired. The difference being that the surface ship now has an exact bearing and range to the submarine rather than only the bearing from which the torpedo originated. The submarine must then immediately evade after firing its torpedoes.

The Russians continue to effectively employ the Oscar II with its SUW missile ranges at 300 NM. The U.S. submarine community is void of any similar SUW OTH capability. U.S. submarines presently have no anti-surface ship weapons other than the torpedo. The Harpoon and the Tomahawk Anti-Ship Missile (f-ASM) are no longer carried on fast attack submarines. The absence of the missiles only tells half the story. The U.S. submarine community, despite its recent commitment to battle group operations, shows little interest in OTH capability. The surface ship community continues to invest money into OTH systems such as Link 11 and Link 16 and Cooperative Engagement Concept (CEC). The surface community is upgrading their Link 11 systems, while the submarine community has no intention of upgrading their own USQ-76 system which is incompatible with the new surface Link 11 system. Although submarines have experimented with Link 16, no submarine has carried the correct equipment to have its fire control system directly interface with Link 16. Link 16 data has to be entered manually by hand into fire control. Link 16 is merely a communication connection exercise. The remaining means of a submarine gaining OTH information from a battle group is via OTCIXS/JOTS, but JOTS data is not meant to provide targeting information-it is mostly used for planning and situational awareness.

This discussion illustrates the difficulty and shortcomings of the surface approach and attack problem using existing submarine equipment, sensors, and weapons. Future options would require equipment not yet developed. In order for the submarine to make an attack from over the horizon, one option is to develop a long range torpedo that could approach quietly with the ability to perform an identification maneuver in which the torpedo proceeded to periscope depth and remotely provided a picture of the target back to the submarine before impact. The torpedo itself could possibly gain targeting information from a satellite during this periscope depth maneuver. The submarine could also be provided real time targeting information from a satellite to employ long range OTH torpedoes or missiles. The submarine must have some form of equipment on board, in either case, to receive OTH targeting information from a battle group or a satellite.

Submarines have successfully employed and controlled Unmanned Aerial Vehicles (UA Vs) within the last two years. What if the submarine could conduct coordinated and simultaneous operations with UAVs and the periscope depth capable torpedo? The UAV could provide the OTH picture and communicate with both the torpedo and the submarine. UAVs have a great potential for the Submarine Force and efforts should continue to develop and test UAVs for such applications.

Another option is to develop a low signature periscope. A departure from the traditional periscopes is required. Any scope like object that sticks three feet in the air must have a minimum diameter to support the forces necessary for the submarine to make headway through the water, but any object of this size will be detected by ARPDD. A low signature periscope could be developed such as a flat mirror-like object that floats on the surface of the water which is able to communicate with satellites in order to paint a picture of the surrounding waters and contact situation.

Technology in the Virginia Class Submarines

Technology continues to influence new construction and how submarines will tight in the future. The application of modem computer technology to weapon systems and sensors, such as the computer technology used in conjunction with the AN/APS-137 radar to create the ARPDD system, raises key questions that should be addressed. What is the impact of using COTS technology in weapon systems? What functions are the computers performing? Are the computers merely being used to speed up the information flow process with the same old processes that were used by the Legacy system, or are the processes being revised to fully utilize the processing power of modern computers? Are the computers being used for more than just information flow? Can we use computers to filter information, discriminate and correlate information, and make decisions that humans once made with the Legacy system? The remaining discussion will focus on these questions.

Submariners are traditionally conservative and feel very uncomfortable about removing the human from the decision making process and replacing him with a computer. However, it is unreasonable for a human operator to sit in front of a radar screen for six hours at a time looking for a radar blip that lasts only ten seconds. It is unreasonable for a sonar operator to stare at a waterfall display for six hours and detect a faint DIMUS trace that might last for three minutes. Conversely, it is also unreasonable for a radar or sonar operator to distinguish, track, and classify upwards of 20 contacts. A sonar narrowband operator is faced with the same overwhelming situation. The correct answer is to let the computer perform this function.

Computers and local area networks offer information at our fingertips. Often, though, the availability of information is overwhelming the operator. The information can be displayed immediately on one computerized flat display in a fraction of a second. ESM bearings, sonar bearings, radar bearings and ranges, and visual bearings are all immediately displayed. Data base management can become impossible to handle when upwards of 100 contacts are displayed. It is information overload, and computers are typically blamed for this problem. The collection of information is only the first level of effectively employing computers in weapon systems. The key to the whole process is knowing when to insert the human operator. Computers are powerful but we must use them properly. Increasing raw information is great, but computers must be employed to provide a second and third level in which the computers correlate, filter, and discriminate.

The ARPDD system offers a prime example of how computing technology can be incorporated into weapon systems. The ARPDD developers recognized that gaining more raw information is not the answer. Radar technology that has been used for years, such as the AN/APS-137, can provide more information than any operator can distinguish. A radar operator has always been able to adjust the gain sensitivity and blank out the screen with radar information. In the ARPDD system, the computers provide a second layer. The computers correlate, discriminate, evaluate, and then deliver a small amount of information that the operator can understand and comprehend. By adding the new computer dimension, the benefit is not necessarily the availability of information but the processing of information.

The Virginia class submarine is the first class of submarines to use COTS computers and hardware for its fire control and sonar systems vice the shock resistant Legacy system. The COTS system is a factor of ten cheaper than the Legacy system (a price tag of $100 million vice $1 billion), but it is not shock tested or proven to survive a close aboard explosion. A change in thinking is required to give up the hardware military specifications (Milspecs) in order to use COTS hardware, but we must demand more of the software developers. How many times has Windows 95 frozen up for the average American, forcing a reboot? The cost savings in using COTS is great and the amount of money necessary for the Legacy system to meet Milspecs is no longer warranted, yet submariners cannot sacrifice survivability for saving dollars.

COTS hardware and software developers are in a highly competitive and fast changing business. The business must perform a financial analysis of how much time the company can afford to spend on creating a bug free product compared to how much profit the company can make if the product was on the shelf in stores. Simply put, the keyword in COTS is commercial. The COTS hardware and software developers are not held to the same standard expected of military hardware and software which has the lives of sailors, soldiers, and airmen depending on its performance. The real issue with using COTS equipment in weapon systems and sensors is not about shock tested but rather performance tested.

It would be prudent to use a portion of the cost savings in buying COTS hardware to ensure a 99.9 percent absence of software bugs and to provide improved algorithms that will enable computers to provide the second and third layers of correlation and discrimination previously discussed. The amount of effort and money in the 1970s that went into developing Milspec hardware should correspond to the amount of effort and money to develop intelligent software that works 99.9 percent of the time. The software should enable the replacement of the human operator from mundane and tedious tasks; it should dramatically increase the information available to the operator; it should correlate and filter; and finally, it should present that information in a format that the operator can easily comprehend. The human must be a key consideration in the software design and engineering, and the human must be placed at the right place in the decision-making.


Focusing on only one system such as ARPDD illustrates the dramatic impact that computer technology will have on sensor and weapon performance. Increased radar or sonar sensor performance will force submariners to change their tactics, equipment, and doctrine. Tactics and doctrine can change quickly, but the development of new equipment to counter the new threat requires forethought, vision, resources, time, and imagination. Aside from the potential threat that ARPDD presents to submarine SUW, the submarine community can draw some interesting parallels from ARPDD with respect to utilizing computers for not only gathering information but to also correlate, sort, make decisions, and reduce the information overload of the operator. Human decision making will always be critical to weapon system success. The challenge in implementing computer technology lies in adequately programming the computer to perform the mundane and highly complex tasks with the human operator intervening at the correct time in the decision making process.

In summary, the following are recommendations that I propose:

  • Introduce the concept of ARPDD in the submarine officer training pipeline at the division officer, department head, executive officer, and commanding officer level. The ARPDD system is only in the development phase, but submarine officers should be introduced to the potential threat that ARPDD offers and how ARPDD affects the traditional surface approach and attack tactic.
  • CNO N87 should invest research and development (R&D) resources to investigate the feasibility of a low radar signature periscope, a long range torpedo with a periscope depth maneuver capability to gain OTH information from satellites, and the development of UA Vs that can provide OTH information to submarines.
  • CNO N87 should invest in a modern OTH weapon and/or return the Harpoon and T-ASM to fast attack submarines.
  • The submarine community must be completely integrated into the battle group Link 11, Link 16, and CEC picture. The submarine community must keep pace with the surface community’s advancement in Link 11. Submarines deploying with battle groups should have the necessary equipment onboard for Link 16 to directly interface with its fire control system.
  • CNO N86 and CNO N88 should fund the ARPDD system to be installed on all USW surface combatants and P-3C aircraft as force multipliers in the battle against the littoral diesel submarine.
  • The design of the Virginia class submarine must employ computers in a manner that not only increase information flow through the sonar and fire control systems, but also provide the necessary software that is 99 .9 percent fault-free with intelligent algorithms and decision making programs that present the increased information in a manner that is beneficial and useful to the operator.

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