A Rationale for Operational Utilization with Concepts for Shipboard Integration
[Editor’s Note: This presentation was made in an unclassified form at the Submarine Technology Symposium on II May 1994.]Introduction
As the priority for U.S. national security continues to shift from conducting global war to containing regional conflict, the focus of naval warfare strategy is changing as well. This is illustrated by the transition of emphasis from open-ocean warfighting capability to joint operations conducted in the littoral (near-shore) regions. As articulated in … From the Sea: Preparing the Naval Service for the 21st Century, U.S. maritime forces will be called upon to provide strategic deterrence, sea control, extended and continuous on-scene crisis response, and power projection-all within the technically and tactically demanding littoral environment. The challenge is to develop new and innovative technological approaches that can support these new missions in a declining resource environment.
This change in warfare priority presents the U.S. Submarine Force with some daunting challenges. Consisting of shallow and confined waters with high shipping densities, the littoral regions are not optimum areas for submarine operations. Maneuvering is restricted and contact detection, classification, and localization are difficult, as is the effective employment of submarine weapons.
While the nuclear attack submarine (SSN) will move forward into the littoral regions and continue to fulfill many of its traditional roles, new and fundamentally different missions will be mandated missions which will continue to take advantage of the SSN’s inherent stealth, endurance, and agility. These new roles are to provide the National Command Authority and any Joint Task Force Commander with:
1. Early, accurate knowledge of the battlefield on which power
may be projected from the sea;
2. Sea-based forces capable of deterring regional aggression or
nuclear attack;
3. Covert striking power against critical targets ashore;
4. Capabilities to enable the establishment of an expeditionary
force on land; and
5. Maritime strength to destroy enemy naval forces and to
interdict seaborne commerce.
The Submarine Force is today, aggressively adapting its operational philosophy and methodologies to support these new roles. However, as littoral warfare requirements continue to evolve and intensify (i.e., more timely and detailed surveillance is needed, more sophisticated strike weapons are deployed, threat offensive and defensive capabilities improve), there must be corresponding improvements in the capabilities of the submarine. Those technologies that enhance the SSN’s ability to observe the adversary (surveillance), influence his thinking (deterrence), and punish him (strike) will become preeminent. In addition, increasing emphasis is being placed on limited strike/low collateral damage, strike warfare, and real-time battlespace surveillance.
Emerging Warfare Requirements
Department of Defense (DoD) technology development emphasis and funding priorities suggest that the future weapon-of-choice in regional conflicts will become the precision-guided, man- in-the loop cruise missile. This statement is substantiated not only by the experiences of Desert Storm, but also by continued funding support for the Standoff Land Attack Missile (SLAM) program and initial funding for the Tomahawk Land Attack Missile (TLAM) Block IV improvement.
While improving overall strike capability for the fleet, the move toward precision-guided weapons will create new challenges for the Submarine Force. Most notably, the inherent Over-the-Horizon (OTH), submarine-to-weapon Command, Control, and Communication (C3) problem must be resolved before submarines can fully exploit the tactical advantages of these advanced weapons. Without the associated capability to update targeting information and/or control the terminal guidance of these weapons in real-time, the SSN strike role, although still viable, may be limited to attacking lower priority targets or conducting second strike follow-ups that do not require on-the-fly re-targeting or man-in-loop terminal guidance. While submarines can support strike warfare in the role of carrying their advanced cruise missiles to the forward area, launching them, and then passing control to another platform, this approach does not reflect a fully optimized employment of SSN forward presence.
Certainly, the submarine has other important roles to play in the littoral regions. These include intelligence data collection, anti-submarine warfare (ASW), anti-surface warfare (ASuW), mine and mine countermeasures warfare, and special operations support. All of these roles, however, imply the ability to detect, goo-locate, identify, and track contacts in the crowded and complex environment near the shore. The common denominator for success in all of these tasks will be the ability to obtain timely, high-resolution surveillance data from beyond the horizon. Accurate and detailed OTH surveillance data will become one of the submarine’s most highly-valued war-fighting resources.
Current submarine OTH surveillance capability is somewhat limited. Beyond direct visual observation, the SSN relies on the monitoring of acoustic/electronic signals and/or the insertion of Special Operations Forces (SOF) to perform this function. These techniques have their advantages, but they also can be recognized as being environmentally limited and not providing the necessary reach for SSN missions of the future. While third-party surveillance data is available to the submarine, it generally lacks the required resolution to support stringent targeting requirements. Additionally, the operational tempo of the submarine must be planned around the schedule of the data sender. Unless a more robust OTH surveillance approach can be developed for the submarine, it will be relegated to support roles that reflect the envelope of its passive sensors.
Worth noting is the fact that the submarine OTH surveillance issue couples back into the submarine strike warfare problem. Given a real-time, high-resolution surveillance capability, a range of new options are created for the SSN in supporting strike warfare. These include monitoring of pre-conflict Indications and Warnings (I&W), Aimpoint refinement, and Battle Damage Assessment (BOA). These capabilities would facilitate the refinement of targeting data for initial strikes and alleviate the occurrences of re-striking targets already destroyed. An effective submarine OTH surveillance capability would serve as an ordnance multiplier.
A conceptual solution to solve the problem of weapon C3 and OTH surveillance is to provide the submarine with an independent capability to launch and control an Unmanned Aerial Vehicle (UAV). As highlighted in the DoD Unmanned Aerial Vehicles (UAVs) 1993 Master Plan, the UAV is a versatile and proven platform for Reconnaissance, Surveillance, and Target Acquisition (RSTA). It can also provide substantial capabilities in Electronic Warfare (EW), Electronic Support Measures (ESM), mine warfare, C3, and special operations. It can readily perform a multitude of inherently hazardous missions and is a viable alternative for littoral missions. Given this rationale for a SUB-UAV, the remaining discussion will focus on issues of SUB-UAV operational benefit, general UAV missions, payloads, communication issues, and three options for shipboard integration.
Operational Considerations
To understand the operational benefit that can be derived from a SUB-UAV, one must appreciate the significant advantage that an SSN’s forward presence can provide, particularly during the early phases of a conflict scenario. A likely sequence of events that could be expected to occur during future littoral conflicts includes:
1. Continuous and ongoing surveillance of an antagonist’s
capability and intent to commit aggression;
2. Covert and aggressive acts by an antagonist which result in
rising political tensions, international warnings, and
economic sanctions;
3. Deployment and build-up of U.S. and coalition forces to
enforce sanctions and prepare for conflict;
4. Open hostilities;
5. Neutralization of the adversary’s capability to make war
resulting with a cease fire or surrender; and
6. Withdrawal of U.S. and coalition forces with continuous
monitoring for compliance with ceasefire/treaty terms.
Without a doubt, one of the earliest players on the scene, and present throughout such a scenario, would be the SSN. With the ability to covertly move into forwarding areas without waiting for the arrival of supporting forces, the SSN is a national asset that can provide early and continuous surveillance of enemy activities. It is the SSN’s stealth and independence and its ability to covertly approach the shore in a pre-and/or early hostilities phase that would leverage the warfighting effect of a SUB-UAV the most. Through the deployment of a SUB-UAV, the SSN could provide early and accurate information on the enemy’s intentions. The SUB-UAV could also allow early strike planning refinement and open the door for submarine preemptive and/or punitive strikes using its own advanced cruise missiles prior to the arrival of other forces. Another important role for the SUB-UAV could be the direct support of Special Operations Forces (SOF). The SSN could inject these forces, launch a SUB-UAV for their support, and then pass control of the SUB-UAV to them.
In light of the third-world proliferation of advanced surface-to-air defense systems and ballistic missile technology, the SSN’s ability to covertly penetrate close to shore could be of critical importance. The SSN may provide the only viable capability to conduct real-time, on-the-scene surveillance in the initial phases of a confrontation before airspace dominance is established. Submarine operations would not be restricted by the long standoff distances required by air and surface forces to protect themselves from missile batteries and weapons of mass destruction. The intelligence data gathered by the SSN could then be passed to the Task Force Commander for further dissemination to his forces. Obviously, as the conflict scenario progresses with allied forces establishing battlespace dominance, the prominence of SSN surveillance lessens. Land-based UAV systems could assume surveillance and data-relay functions. The SSN strike role, however, could remain viable through connectivity with those land-based UAV systems.
Any approach for analyzing the benefits of a SUB-UAV should correlate established UAV missions with desired SSN roles. While this approach suggests that substantial benefit could be gained from a SUB-UAV, further analysis which defines specific Measures of Effectiveness (MOEs) should be performed. As an example of the quantifying analyses needed, imagine a hypothetical scenario in which 100 advanced cruise missiles are to be fired in an initial attack preceding massive airstrikes. If the surveillance and Aimpoint refinement provided by a SUB-UAV in a pre-hostilities environment increases strike effectiveness by 10 percent, what would be the impact? It could be surmised that as many as ten weapons would be saved in the initial strike. Likewise, the additional missiles that would be required for the re-strike of missed targets would be saved. This represents cost savings for inventory replenishment. It also increases flexibility for future strike planning by preserving assets in the forward area. Reduced attrition of aircraft during the subsequent airstrikes would only amplify the benefit of this increase in strike effectiveness.
There are, of course, trade-offs that must be accepted in implementing a SUB-UAV system. Any analysis, as detailed above, would also define the penalties for such a concept in a quantitative way. Some of the obvious detractors to the concept include:
1. Reduction of submarine stowage space for weapons;
2. Inability to recover the UAV results in a high-cost
permission and risks capture of the unit;
3. Additional onboard equipment/systems are required for
UAV mission planning and communication and control;
4. Increased submarine vulnerability/detectability during launch
and communication with the SUB-UAV; and
5. Increased manpower/training requirements.
A final detracting argument that can be raised is that orbiting satellites negate the need for a SUB-UAV. Certainly, satellites possess communications relay capabilities and surveillance features. The key issue, however, is the SSN’s accessibility to what the satellite can provide in real-time. Given that a satellite asset is available, that the SSN’s operational tempo can support that satellite’s orbital and communications schedule, and that the submarine retains dedicated access and priority, satellite utilization could support many of the roles suggested for the SUB-UAV. However, due to the high demand for satellite resources expected during periods of increasing tension and conflict, it is unlikely that all of the criteria listed above could be consistently met. Additionally, the flight and arrival of a SUB-UAV could not be predicted in the same way as the overflight of a satellite. The adversary would not have the advantage of clear sky periods to conduct operations when surveillance satellites are not in position.
Given that a SUB-UAV would enhance the SSN’s capabilities in the littoral environment, a preliminary listing of desired operational characteristics can be defined for it. The ideal SUB- UAV capabilities needed to support the requirements defined above would include:
1. Compatibility with existing submarine launcher systems;
2. 10 to 12-hour flight endurance with a minimum 75 kt speed;
3. 50 to 75 lb payload capacity;
4. Size and geometry which allows tandem stowage in torpedo
room (i.e., stow two SUB-UAVs per weapon stow position);
5. Command and control system compatibility with UA V base
line data link;
6. Configurable payloads that could be changed on-board the
submarine;
7. Minimized need for a submarine to remain at periscope depth
during SUB-UAV flight;
8. Compatibility with existing SSN equipment for SUB-UAV
mission planning and control; and
9. Recoverable (either the SUB-UAV with its payload or just
the payload alone).
UAV Issues
In examining the concept of a SUB-UAV, it is useful to examine proposed SUB-UAV missions in light of current UAV program planning, payloads, and command and control data links. A general discussion of these UA V issues is provided here, as adapted from the DoD Unmanned Aerial Vehicles 1993 Master Plan which is published by the Program Executive Office, Cruise Missile and Unmanned Aerial Vehicles Joint Program Office in Washington, D.C. The reader is referred to ‘that document for more detailed information.
Based on the discussion in the “Operational Considerations” section, a listing of some of the more prominent missions would include:
1. Surveillance and Reconnaissance;
2. Pre-Conflict Indications and Warnings;
3. Aimpoint Refinement for Cruise Missile Strike;
4. Relay for Weapon Command, Control, and Communication;
5. Battle Damage Assessment;
6. ASUW Detection, Identification, and Localization;
7. ASW Surveillance;
8. Mine Field Identification and Localization;
9. Special Operations Support;
10. Electronic Warfare and Electronic Support Measures;
11 . Air Strike Support;
12. Environmental and Atmospheric Monitoring; and
13. Cease Fire and Treaty Compliance Monitoring.
Without a doubt, the heart of the UAV is its payload. Multi mission payloads provide UAV systems with the capability to simultaneously perform missions of Reconnaissance, Surveillance, and Target Acquisition (RSTA}, Electronic Warfare (EW}, and communications relay. The UAV Joint Project Office (JPO) is monitoring and coordinating such multi-mission payload development efforts for future UAV integration. The following summary provides descriptions of a number of UAV payload efforts that would be of interest for a SUB-UAV concept:
1. Lightweight Common Forward Looking Infrared (FLIR) A FLIR is the primary imaging sensor for the UAV in performing RST A functions. Recent advances in FLIR technology allow better sensitivity and greater resolution, resulting in improved performance. In addition, multi-spectral coverage will improve target detection capability and aid automatic target recognition and cuing.
2. Moving Target Indicator (MTI) Radar-This is a radar payload capable of detecting and automatically tracking moving targets and classifying moving vehicles. It incorporates a spotlight mode Synthetic Aperture Radar (SAR)/- Inverse Synthetic Aperture Radar (ISAR) to detect stationary targets by highlighting small, selected areas individually. It can be used for surface sea search to track ship formations with the ISAR mode being used to highlight individual ships for target identification.
3. Multichannel UHF/VHF Communication Relay-This payload will support a communications relay capability that will extend communication ranges and overcome horizon limitations. The UAV JPO plans to develop a lightweight, miniaturized five-channel Very High Frequency/Ultra High Frequency (VHF/UHF) relay to satisfy multi-service needs.
4. Mine Countermeasures (MCM)-This development effort addresses a mine countermeasures payload that can detect and localize mines in the surf zone and in shallow water.
5. Electronic Countermeasures (ECM)/Decoy-This ECM-/decoy payload will have the ability to disrupt/harass/deny operation of the enemy’s communication systems and radars. The payload includes a Very High Frequency (VHF) noise jammer, a High Frequency (HF) jammer, a VHF frequency hopping jammer, and a radar jammer.
6. Signal Intelligence (SIGINT)-This payload provides a SIGINT capability for intercepting and locating enemy communications and providing non-obtrusive monitoring of potential adversaries in peacetime. It will include an Electronics Intelligence (ELINT} system capable of intercepting and locating enemy radars to provide information concerning the enemy’s electronic order of battle.
7. Self Protection Radar-Warning Receiver Jammer/Decoy Payload-This payload will improve the survivability of future UAVs in a hostile and saturated air defense environment. This system would operate in several modes by providing radar/missile warning, self-screen jamming, and electronic decoy functions.
8. Meteorological (MET) Sensor-This development effort will result in a lightweight Meteorological (Mel) payload which can measure temperature, humidity, and atmospheric pressure and will contain software for computation of wind velocity using UAV navigation data.
9. Chemical Agent Detection-This payload uses an interferometric Infrared (IR) sensor to analyze chemical agent clouds. It would provide a standoff capability in alerting military forces of chemical munitions events.
A final important issue for SUB-UAV utilization would be its C3 data link. Because current submarine communications systems do not support the designated baseline data link for UAVs (the AN/SRQ-4), a specific method of SUB-UAV command and control remains undefined. Development of a new and unique submarine-lo-U A V data link is not desirable because of the established and fundamental communication requirement that UAV control stations universally be able to control, receive, and exploit mission data from different platforms. The control of data link growth is a key issue for maintaining universal U A V connectivity.
Future options for data links are being considered by the JPO. A modification of the Common Data Link (COL) used by the Medium Range (MR) UAV is under study by JPO to augment the existing baseline architecture for future UAV upgrades. Several proposals for a modified Joint Tactical Information Distribution System (JTIDS) data link has been put forward. All of these, however, do not solve the basic submarine equipment and antenna incompatibility problem. A better approach may lie with data modification techniques. A new concept proposes a compression/decompression technique for IR imagery that would allow the use of standard 16 kilobyte digital UHF voice radio circuits. This UHF technology applied as a SUB-UAV data link would result in both equipment size reductions and the elimination of specialized hardware. Quality images provided at a usable rate for target identification on existing UHF radio circuits would be the result.
Submarine Integration Issues
Providing the SSN with a SUB-UA V capability would not be a trivial task. The primary challenge would be to package the UAV within a 21-inch diameter cylindrical envelope in order to allow launcher system compatibility. A second important consideration would be providing the UAV with the capability to travel underwater to the surface so it could then transition to flight. A final important issue would be providing the submarine with a means to perform SUB-UAV mission planning and command and control.
The integration of cruise missiles into submarines does set a precedent for accomplishing these goals. Two basic approaches have been used for missiles. The first, used for the Harpoon missile, is to encapsulate the weapon in a buoyant capsule so that it remains dry during an unpowered but controlled trajectory to the surface. Upon capsule broach, a nose cap flies off and the missile is booted out by a rocket motor allowing fin deployment and engine start. In the second approach, used for Tomahawk, the missile is launched into the water environment where a booster rocket motor ignites and then propels the weapon to the surface and beyond in a controlled fashion. Wing deployment and engine start then occur in the air. Based on the techniques used for cruise missiles, two SUB-UAV integration options become apparent.
The first option would be to design/adapt a UAV to fit inside the existing Harpoon capsule. It then could be launched and transition to flight in much the same way as the Harpoon missile does. A SUB-UA V with an X-wing design (one in which the airfoil surface pivots on its center at an attachment point on the fuselage) would allow the wing to be stowed parallel to the longitudinal axis of the SUB-UAV. In this manner, wingspans of up to 15 feet could be accommodated. However, a restrictive 18-inch capsule inside diameter would limit fuselage size and airfoil width. The design would also have to accommodate a folding prop with a universal joint attachment to the engine. A small booster rocket motor would also be required to power the SUB- UAV up and away from the capsule after surface broach. Large enough to push the SUB-UAV to sufficient altitude for wing/prop deployment, aerodynamic stabilization, and engine start but not so energetic as to damage the unit with violent acceleration, the booster design would be critical. The design would have to account for the fact that, during boost, the SUB-UAV would experience velocities much in excess than those of normal flight and could result in aerodynamic damage or instability. An aerodynamic sheath might be required which would fall away after boost velocity decreases. Also important would be the unit’s control system that could sense airspeed and altitude to properly time wing deployment, booster release, and engine start. If these design challenges could be met, the advantage of existing Harpoon capsule compatibility with the SSN would greatly facilitate the integration for submarines with 21-inch torpedo tubes. Unfortunately, no U A V in the current inventory would lend itself to easy adaptation for this concept. Given the combined cost of a Harpoon capsule and a unique SUB-UAV design effort, this approach would be costly. Additionally, the restrictive interior dimensions of the capsule would limit SUB-UAV size and therefore, payload lift capacity.
A second option would be to adapt the existing Tomahawk missile to accommodate a dedicated UAV sensor/communications payload in place of its warhead. It could be loaded and launched in exactly the same manner as a tactical Tomahawk missile in either vertical or horizontal launch tubes. This would provide a capability, not unlike that of the existing MR UA V and immediate submarine compatibility for loading and handling. MR UAV capabilities address the need to provide pre-and post-strike reconnaissance of heavily defended targets and to augment manned reconnaissance platforms by providing high quality, near-real-time imagery. The MR UAV differs from other UAVs in that it is designed to fly at high subsonic speeds and spend relatively small amounts of time over areas of interest. A disadvantage of this approach for the submarine would be the unit’s relatively limited “on station” time for applications as a communications relay. Another disadvantage would cost. The use of a Tomahawk airframe adapted to carry a sophisticated UAV payload would likely be cost prohibitive. It should be noted that current proposals for the Tomahawk Block IV improvement include a capability to relay surveillance data to the Task Force Commander via satellite during inbound flight to attack targets. This would allow in-flight BDA; however, it means that an attack must be in progress before any surveillance data can be gathered.
In implementing either of the above integration concepts, it can be seen that many of the ideal operational characteristics for a SUB-U A V, as described in the Operational Considerations section, would not be provided. Additionally, it is likely that the cost and effort to implement either approach would be considerable. For this reason, a third concept which starts with a clean sheet of paper to address the stated requirements will be described. The ability to recover the SUB-UAV, or at least recover its payload, would be best addressed by a Vertical Takeoff and Landing (VTOL) capability. Several prototype configurations for VTOL UAVs have been evaluated by JPO. The most applicable VTOL design for a SUB-UAV is the Maritime Vertical Takeoff and Landing Unmanned Aerial Vehicle System (MA VUS). Basically a small, unmanned helicopter, the MAVUS is comprised of a Power Module {with gas turbine and integral differential/reduction gearbox), a Propeller Module (with transmission and dual counter-rotating hubs with three rotor blades each), and a Payload Module {which can accommodate payloads for Day TV, ESM, Communications Relay, or FLIR). With modifications to increase its flight endurance {currently 2.5 hours), reduce its body diameter (currently 25 inches), and allow folding of its rotor blades, a modified MA VUS with an associated launch capsule could address most of the SUB-UAV requirements described in the Operational Considerations section. The following design concept presents the basic operational sequence for system deployment and use.
Prior to launch, the SUB-U A V (with folded rotor blades) would reside in a 21-inch diameter capsule with a length of no more than 10 feet. This would allow ejection from standard diameter, horizontal torpedo tubes and accommodate tandem rack stowage. Removable, watertight panels on the capsule would allow crew access to the Payload Module so the SUB-UAV could be configured for different missions. Also in the capsule would be a transmitter and antenna module which would provide the radio communications link to the SUB-UAV during flight.
Once in the torpedo tube, an umbilical cable would provide initial operating power and allow monitoring of internal functions to satisfy launch interlock requirements. Data communication for navigation/payload initialization and mission plan download would be provided via fiber optic cable. After launch, the positively buoyant capsule would transit to the surface and be ballasted to float vertically. The SUB-UAV would be on internal battery power at this point but continue to maintain communications with the submarine via the fiber optic cable which would deploy from a spool in the torpedo tube. The payout of fiber optic cable would allow the submarine to maintain communications with the capsule transmitter/antenna module and thus communicate with the SUB-UAV while submerged. Limited maneuvering of the SSN would also be possible during the flight of the SUB-UAV.
On the surface, capsule buoyancy and stability would be augmented by an inflatable collar. Upon command from the submarine, a capsule nose cap would fly off and an internal platform would push the SUB-UA V upward to a position that would allow the rotor blades to unfold and lock in position. On command, the unit engine would start and the SUB-U A V would lift off the capsule platform to complete its mission. If available, a surface ship could provide recovery services for the SUB-UAV. It would then be possible to refuel and re-deploy the unit with an
alternate payload if so desired.
Command and control data generated by the submarine operator would be passed to the UAV via the fiber optic cable and capsule transceiver/antenna module. Data from U A V would pass to the submarine via the reverse path. The SUB-UAV could also up-link data directly back to the Task Force Commander. While this communications approach would require submarine modifications to accommodate the fiber optic cable and its spooling mechanism, it would solve the data link problem with regard to communications equipment and antennas.
Current plans call for MA VUS mission planning to be hosted on the USN Tactical Advanced Computer-III (T AC III). This computer is now being deployed on SSNs and would support SUB-UAV mission planning and control. Given the planned universal connectivity planned for UAVs, control of the SUB-UAV could be passed to a third party.
It should be noted that the current MA VUS design would require significant modification to fit within a 21-inch diameter capsule. The new design would also have to accommodate increased flight endurance requirements and address capsule stability issues for launch from the sea surface. While this design would result in a new and unique maritime UAV for submarine applications, the new system would be compatible with and support surface ship applications.
Summary
The U.S. Submarine Force faces new challenges as the emphasis on littoral warfare continues to grow. These challenges will demand new ways of thinking and new technological solutions. As the development of advanced, precision·guided cruise missiles progresses and these weapons transition into the fleet as operational systems, the capability of the submarine to effectively utilize them must keep pace. This means that submarines must be able to survey target areas in detail and then communicate with their weapons at long ranges. An option that can satisfy this requirement is to integrate a SUB-UAV capability into the submarine. While imposing significant technological challenges, a SUB-UAV integration effort is no more daunting than the challenges posed and met 20 years ago in integrating air-breathing cruise missiles into submarines. Unless the Submarine Force is provided with a SUB-UAV system or an alternative system that provides equivalent capabilities, its role in littoral warfare will diminish.
REFERENCES
1. From the Sea: Preparing the Naval Service for the 21st
Century, September 1992
2. Submarine Force Vision, 30 June 1992
3. Department of Defense Unmanned Aerial Vehicles (UAV)
Master Plan, 31 March 1993
