Application of Guns in Naval Force Protection

NAVAL ENGINEERS JOURNAL WINTER 2002■51The modern designs include:■Medium caliber with high rates of fire,e.g.,1000 rounds per minute (RPM)■Extremely accurate fuse technologies combined with muzzle velocity measure-ment and correction calculations that per-mit densely delivered payloads.■Air bursting ammunition with high lethal-ity from tailored sub-projectile pay loads that is also impervious to ECM/decoys.■Extended engagement ranges from two to six km.A combination of all these features offers a lethality mechanism to defeat any threat by delivering a dense wall of steel between the ship and the threat target.Independently verified modeling has shown that these modern gun systems are able to engage ten targets with a maximum keep-out-range of 2600 m.The Close in Gun System (CIGS) ScenarioTen radially inbound small craft traveling at 40 knots over calm seas, which have sur-vived the outer layer of defense, are to be prevented from closing to within 1000 yds of the ship. The threat can occur duringeither day or night. The ten craft are distrib-uted inside a 90-degree arc and a 300-yard range band. The baseline target is a “ciga-rette boat” which is 12 m long, has a 2.6 m beam and a 0.9 m draft and/or “jetski”approximately 3 m long.Based upon an Office of Naval Intelligence (ONI) threat assessment, the Naval SeaSystems Command (NAVSEA) invited inter-ested parties to provide information concern-ing existing development efforts for a weapon system capable of defeating thethreat. This weapon system may be installed on any surface ship including coastal patrol craft, Coast Guard cutters, destroyers, cruis-ers, and amphibious warfare ships. This effort is known as the CIGS Study.The purpose of this paper is to examinemodern naval gun designs that are applicable to the asymetric and “leaker” threats. The paper will not attempt to address a “system high” solution; a solution that addresses all elements necessary to defeat the threat, i.e. ,detection at range by surveillance sensors,threat evaluation and handoff to fire control sensors, computation of the fire control solu-tion, weapon assignment, weapon engage-ment, assessment of target distruct, and weapon cease fire. It is the opinion of the author that the detection, tracking, and com-putation components of a gun weapon sys-tem are well known off the shelf capabilities.Application of Guns in Naval Force Protection■Andrew BradickABSTRACTAny warship operating in a littoral environment is highly susceptible to attack from surface raider craft — the so called “Boghammer” threat. The NAVSEA close in gun system (CIGS) requirement stipulates a ten target scenario based on ONI analysis. The purpose of this paper is to discuss those sub-elements of a gun-based system that in combination will maximize performance by minimizing engagement time per threat. Modern gun and ammunition designs offer a new option for multipurpose self-defense on all classes of combatant ships as well as an effective and economical solution to their inner layer defense requirements.T E C H N I C A L P A P E RThis paper was presented during ASNE Day 2001 on Tuesday,May 1st.Further, the systems approach has in the past prevented an objective analysis of apples to apples, or in this case, gun to gun. Suffice it to say that modern sensors and systems using industry or military standards in the design and construction of all hard-ware and software elements will allow any gun to integrate with all the other elements of a weapons system.Historical ReviewThe following is a brief review of the recent past leading up to the current status, fol-lowed by the identification of the relevant elements of gun design as they relate to defeating the threat.This paper does not address ILS issues because of time and space constraints.The data presented is based almost exclu-sively on simulations and analysis since bud-get priorities have not included this require-ment. However, it is hoped that what is pre-sented will stimulate others who can provide the resources needed to get beyond this point.The following events listed are the most recent minor caliber gun studies and require-ments. The first of the recent studies/pro-grams, the advanced minor calibre gun sys-tem (AMCGS), was meant to identify a replacement for the 3”/50 gun.■AMCGS1992■USCG SSWS1994■SWPS Study Dahlgren1994■NAVSEA SSPS1996■NSIA SSD Study1996■Louisville RFI1997■PacFleet MNS1999■NAVSEA CIGS Study1999■NDIA ASUW Study1999In 1994, the Coast Guard reiterated to CNO N86 its long standing requirement for a shipboard stabilized weapons system (SSWS). This requirement was one of the first times that the susceptibility to attack from surface raider craft (Boghammer threat) and the establishment of a 1000 yd “keep out” range were noted. The Coast Guard also provided an analysis of the “shots to kill” for emphasis.In 1996 and 1997 there were several more studies launched. In 1999 PACFLEET sent a mission needs statement (MNS) to CNO N86 for a naval close-in gun system noting that:“Defense against multiple small, high-speed, maneuverable surface threats and slow, low flying aircraft is critical to control and sus-tainment of presence especially within the littoral. The development of an automated minor caliber gun system to counter threats that may leak by existing larger caliber gun systems is a critical warfighting equipment.”PACFLEET went on to describe the require-ments as: “ …accurate, electro-optical, stabi-lized, multiple-track weapon system with the capability to detect, identify and engage with sufficient lethality to destroy existing (and) projected mobile, high-speed threats that may leak by existing naval gun systems and armed helicopters. An advanced minor caliber gun system will provide the capabili-ty within the practical range of 25 mm to 40 mm ammo.”The specific performance characteristics were:■Range: 4,000 meters;■Day/night/all-weather sensors;■Systems must not hinder operation of the main battery;■Embedded training;■System must be capable of being brought into action quickly (5-20 seconds) andremain in a ready state indefinitely;■System must be capable of remote or local operation (fully mechanical) in theevent of a system interface failure;■The system will comply with all applica-ble safety, health, and environmentalrequirements.Base Line ConfigurationThe desired weapon system was initially characterized in the base line configuration shown below:Application of Guns in Naval Force Protection52■ WINTER 2002NAVAL ENGINEERS JOURNAL■Two axes stabilized (minimum);■Remotely controlled, with man-on-the-mount capability desirable;■Not integrated into the ships combat sys-tem;■Does not penetrate the deck (except for power and control cables;■Operates from ship’s AC power with backup power capable of completingengagement against the threat;■Working circle of less than 20 ft (6 m) and less than 8 ft (2.4 m) in height;■Capable of being fired by one person and maintained/loaded by two personnel;■Includes an electro-optical sight for day/night operations and capability toprovide range and ballistic computations and corrections;■Operates in sea state three and survives insea state five.The CIGS Study Team developed an evalua-tion matrix shown in Table 1based on Fleet,lab and staff inputs. The column headedPre-Study Composite Inputs is arranged bypriority 1 through 22 based on the inputsfrom USN Fleet, lab and staff responses. It isintersting to note that no single elementachieved a significant concensus, e.g., thenumber one element only got 20.17%. Thismatrix was used to evaluate the 13 industryinputs to the study’s request for information(RFI). In the course of the study, additionalfactors were noted and were added as“Newly Identified” at the bottom of Table1. Certain conclusions were highlighted askey findings as shown in the column labeledPost Study Conclusion. For the purpose ofApplication of Guns in Naval Force ProtectionNAVAL ENGINEERS JOURNAL WINTER 2002■53this paper, a fourth column labeled Performance Criteria was added to further refine the data to specifically those that bear solely on defeating the threat.The 22 criteria established a good base line considering the limited time and budget available. It must be recognized that there was no original work/research as an objec-tive of the study. It was, in fact, a review of industry inputs that attempted to evaluate the submissions by applying criteria that evolved from ONI, the Fleet, and OPNAV. It is suggested that the constraints of the study prevented any “drill down” into the data. The “system high” approach led to an over-all conclusion that there were no proposals which satisfied the CIGS requirement to defeat ten simultaneous surface threats before a 1000 m keep out zone.There was, however, one conclusion that urged further examination. The performance of air bursting munitions (ABM) was impressive enough to be called out as hold-ing promise as a potential solution. It is important to note here that this conclusion seems to supersede a Fleet imposed criteria that the ammunition for the CIGS solution already exists in the Fleet.If the focus is on a minor calibre gun solu-tion as proposed in the CIGS study for rea-sons of cost, weight, space, etc., it is possible to examine the various parameters in isola-tion for clarity.Application of Guns in Naval Force Protection54I WINTER 2002NAVAL ENGINEERS JOURNALFIGURE 1:CIGS Scenario Time and Distance FactorThe graph shown in Figure 1is an attemptto depict the constraints on this dynamic scenario. The performance of each gun would be plotted on the X and Z axes. The X axis would be bounded on the far right by the maximum effective open fire range of the gun being measured and on the near right by the keep out range of 1000 yards. The Z axis is the measure of the specific gun performance combining both rate of fire and the lethality of the ammo fired by the gun, i.e., how many rounds are needed to kill the target at range. The Y axis depicts the time available to defeat the ten targets. Time is solely a function of the open fire range of the specfic gun. Therefore, the graphic in the X-Y Plane represents the total time available to defeat the ten targets.Note the time and distance factor. With a keep out range of 1000 m, a maximum effective range of 20 mm-40 mm cannon between 2500 and 4000 m, a closing rate of 20 m/sec (40 kts), and a ten threat scenario requires a solution within 75-150 seconds or approximately 7.5 to 15 seconds/threat.The elements that have claim to the time components are■Detection■Tracking and computation■Threat evaluation and weapons assign-ment■Target engagement and defeatTable 2combines these elements into three principal events and assigns a time budget to each event.Detection — at the engagement ranges man-dated by gun performance, the detection of the threats are well within the capabilities of installed surface search radars and there-fore do not have any claim on the time bud-get.Tracking and Computation and Threat Evaluation and Weapon assignment—These two functions are usually combined into a single “control” function. Summing up the sub elements, an estimate of five seconds per threat may be used for the “control” function.Therefore, the result is an average engage-ment time of 2.5 to 10 seconds per targetdepending on the effective open fire rangeof the cannon.Before proceeding, it must be decided whatit is we hope to achieve during this engage-ment time.The advent of the anti-ship cruise missile(ASCM) and the development of the closein weapons system (CIWS) to counter thisthreat made the absolute destruction of theASCM mandatory because of the extremelyshort engagement range inherent in the 20mm caliber gatling gun and the extremelethality of the ASCM. With the scenario oflarger calibers and slower threats, it is pos-sible to consider other “kill” levelsdescribed in Figure 2 such as C — instantmission kill, i.e., the threat can no longerpress home the mission and is therefore nolonger a threat.Current StatusAs a result of a follow-on study to CIGSsponsored by National Defense IndustriesAssociation (NDIA), there is further evalua-tion of the performance of gun systemsagainst the ten threat scenario.NDIA ASUW Study: SC21 COEA AnalysisModel■MK 46 30mm with conventional ammu-nitionApplication of Guns in Naval Force ProtectionNAVAL ENGINEERS JOURNAL WINTER 2002■55■MK 46 30mm with ABM ■Phalanx 1BUsing the SC21 COEA analysis model,NDIA assessed the effectiveness of theMK46 30 mm weapons system (AAAV tur-ret) using both conventional and air bursting ammo and the Phalanx 1B.In brief, the MK46 with conventional ammo was not effective against the threat; howev-er, when the MK46 used air bursting ammo,it was able to defeat eight of the threats (before it ran out of time). The Phalanx,although open fire range was much less,managed to defeat seven threats (before itran out of ammo).The lessons learned from these simulations were that air bursting ammo significantly enhances the defeat mechanisms of the minor calibre gun and in the case of the Phalanx, the high rate of fire is a significant factor in defeating the threat.Desirable characterisitics identified by these studies can now be summarized and further refinements suggested:■Air bursting munitions (ABM)■High rate of fire■Max effective open fire rangeIt can be concluded at this point that:■Air bursting ammo increases the effective-ness of each engagement by increasing the number of hits per round.■High rate of fire increases the effective-ness of each engagement by reducing the time per engagement.■Extending the open fire range as a gun characteristic would translate into added time to permit the defeat of all threats before the keep out range of 1000 m.Having identified certain characteristics of gun systems that point to a successful com-pletion of a CIGS scenario mission, it would be appropriate to look at additional refine-ments and describe a base line for the defeat mechanism. The time critical nature of the problem may be described as putting theApplication of Guns in Naval Force Protection56■ WINTER 2002NAVAL ENGINEERS JOURNALKK - KILL the threat will be defeated immediately after being hit!K - KILL the threat will be defeated within 30 (s)after being hit!A - KILL the threat will be defeated within 5 (min)after being hit!B - KILL the threat will be defeated within 30 (min)after being hit!C - KILL(mission abort kill) after being hit, thethreat will not be able to complete the mis-sion!FIGURE 2:Target Kill CriteriaFIGURE 3:ABM Projectilemaximum effective energy on target (space)in the minimum time. Using a time/space measurement will help to provide discipline to the process. For example, it is fairly intu-itive that if a Boghammer/jetski target could be hit with one 40 mm point detonating high explosive (PDHE) round the threat would no doubt be destroyed or seriously disabled.The realities are that multiple error factors of sensor system, fire control, weapon and ammo all conspire to make the desired “one-round-one hit” a statistical improba-bility because of■Angular dispersion,■Round to round muzzle velocity (M.V .)error, and ■Range dispersionsThese facts of life require multiple rounds to ensure that a statistical hit will occur.Ideally then what is sought is a burst of fire that would deliver maximum energy, concen-trated in both time and space. This defeat mechanism has the added advantage of mini-mizing the number of rounds required to defeat each threat and inversely, increasing the number of engagements each gun is capa-ble of performing without reloading. Each desirable characteristic will be exam-ined beginning with the air bursting ammo,since it seems to enjoy the approval of both the CIGS and NDIA studies. Air bursting ammo has been around for a long time in the Navy in the form of both mechanical time (MT) and variable time (VT or proxim-ity) fuzed fragmenting high explosive (H.E).The principal shortcoming of these designs lies in the fact that under best-case condi-tions, they deliver less than 25% of the pay load to the target. Newer designs such as the projectile in Figure 3use pre-formed pay loads that deliver the sub-projectiles uni-formly across a plane ahead of the target.This design uses an electronic time fuze that activates a small ejection charge. The charge provides over pressure in the interior of the outer shell causing it to peel away from the sub-projectiles. The sub projectiles, now unrestrained, utilize the longitudinal and rotational vector from the projectile to dis-tribute themselves. As seen in Figure 4this distribution permits a theoretical 100% of the sub-projectiles to intercept the target.Keeping with the ammo element of thedesirable characteristic, we can consider fur-ther design refinements where we maximize the pay load by using the conserved energy of a high muzzle velocity round in lieu of a bursting high explosive (H.E.) charge. This has the collateral benefit of increasing the safety of the round by virtually eliminating any H.E. in the projectile.Based on the CIGS threat characteristics and vulnerabilities an assessment was made of the lethality level requirement for a 90%mission kill probability using three gram cylindrical sub-projectiles.Table 3represents minimum levels of hitdensity needed to cause damage to mission critical systems and personnel for 90%mission kill probability in the Analytic Performance Model.The photo in Figure 5 demonstrates the results of a live firing as proof of concept.Another refinement would be to incorpo-rate a fuze design that would dispense the pay load at a predetermined distance from the threat, tailoring the density of the sub-projectiles to factors such as target range,fire control accuracy, target hardness etc.Finally, to minimize dispersion in range,thereby concentrating the delivered energy in space, we would want to incorporate muzzle velocity correction. Figure 6describes the mechanization of round byApplication of Guns in Naval Force ProtectionNAVAL ENGINEERS JOURNAL WINTER 2002■57FIGURE 4:Single Round Sub Projectile Patternround MV correction using a muzzle veloc-ity measuring muzzle brake and electronic fuze programming.Figure 7demonstrates the practical effectof on-line compensation of round by round muzzle velocity error correction.The gun characteristics of high rate of fire and maximum effective open fire range are in the first instance meant to minimize the time of each engagement and in the second to increase the amount of time available for the total engagement.The two common cannon configurations are the single barrel sliding breach or chain gun designs that have rates of fire from 175 - 400 shots per minute and the CIWSusing a multi-barrel gatling gun design to achieve rates of fire of up to 4500 shots per minute. The conventional gun’s rate of fire as previously discussed, is not ade-quate to address the ten threat scenario before time runs out. The gatling design brings with it a serious weight and com-plexity penalty.Figure 8illustrates a third alternative ofproven design and operational history. The four chamber revolver cannon achieves a rate of fire 1000 shots per minute without any weight or complexity penalty.The Way ForwardThe original CIGS scenario and the crite-Application of Guns in Naval Force Protection58■ WINTER 2002NAVAL ENGINEERS JOURNALTable 3Conditions for a 90% Mission Kill RANGEHIT DENSITY OF MINIMUM SUB-CUMULATIVESUB-PROJECTILESPROJECTILE PENETRATIONPENETRATION OF SUB-PROJECTILES(m)(Sub-Proj/m2)(mm Alum.Alloy)(mm Alum.Alloy/m2)10006211262000716112300081296400010880FIGURE 5:8 Rounds at 1600 mm Aluminum Deckhouse (Boghammer Style)ria developed from the study to confirm that all of the elements are in hand to defeat the 10 boat threat must be evaluat-ed. At the beginning of this paper, it was stated that our purpose was to focus on the characteristics of a gun system needed to defeat the threat.It must once again be stipulated that the characteristics needed for detection andcontrol as listed below are readily available.Detection and Control■First detection– Conventional 2D/3D surface search radar■Threat evaluation and weapon assignment– Either an integrated part of the combat system or a module on the gun mount.■Tracking sensor– Stand alone or mounted on the gun mount– EO FCS able to acquire and track automatically (auto track)– FLIR/video/LRF– Lead angle and ballistic computation either in the sensor pack or on the mount moduleCurrent architecture is completely “open” and system integration would be straight forward.All of the desirable gun characteristics iden-tified in this paper are summarized below:■Air bursting ammo ■High rate of fire■Low Dispersion (M.V . correction)■Short time of flight = high M.V .■Maximum effective open fire range ■Fuze accuracy ■High energy payloadApplication of Guns in Naval Force ProtectionNAVAL ENGINEERS JOURNALWINTER 2002■59FIGURE 6:Tailored Fuze Activation and M.V.CorrectionIncorporating all of their characteristics in to a minor caliber gun produces the analyti-cal results illustrated in Figure 9for the CIGS scenario.Two possible scenarios are illustrated at max-imum range and minimum range in order to highlight the fact that the “rounds per kill” in this dynamic scenario is range dependent.The following assumptions were made in this illustration:■Thirty-five mm airbursting ammo for lethality and range.■Revolver cannon for high rate of fire.■Target speed and size per the CIGS study.■A five second time budget to perform the detection and control function.■Engagements are “fire and forget”.■A desirable P .K. of 0.9.To illustrate the sequence of events shown in Figure 9, consider that the first of the ten engagements begins at the maxiumum effec-tive open fire range of the 35 mm cannon (3500 m). At this range, analysis indicates that 24 rounds would be required for a mission kill. The time required is 1.45 sec-onds using a rate of fire of 1000 ing the established target sequence of five seconds per target, the second target would have advanced 40 m/sec x 5 sec or 200 m so that the second engagement would occur at 3300 m. At this range,analysis predicts that the 35 mm revolver cannon firing ABM would require 18rounds or approximately 1.1 seconds. The remaining engagements would follow suit.Table 4offers a comparison of the perfor-mance of other gun systems. Estimateswere made based upon data available from open sources such as Jane’s, the known physics of gun performance, and optimum “rough-order-of-magnitude” figures.Application of Guns in Naval Force Protection60■ WINTER 2002NAVAL ENGINEERS JOURNALFIGURE 7:On-Line Compensation of Muzzle Velocity VariationNAVAL ENGINEERS JOURNAL WINTER 2002■61Application of Guns in Naval Force ProtectionFIGURE 8:Four Chamber Revolver CannonFIGURE 9:(left)35 mm ABM T en Surface Intruder CraftEngagement and DefeatConclusionThere exists today proven gun and ammo technologies that in combination will readily defeat the CIGS scenario threat.There do remain other operational and tech-nical issues not covered in this paper.However, the author is confident that these are readily addressed, e.g:■Reload in the heat of battle ■Mean time to repair (MTTR)■Cost/kill■Total ownerhip cost (TOC)AcknowledgementMr. Wayne Schneider PMS 529. ■BIBLIOGRAPHYNAVSEA PEO TSC Close-In-Gun System Status and RFI Results, August 3, 1999NDIA SUW Study as of December 17,1999Jane’s Naval WeaponsApplication of Guns in Naval Force Protection62■ WINTER 2002NAVAL ENGINEERS JOURNALMR. ANDREW BRADICK holds a BSME from Stevens Institute of Technology and is a graduate of theU.S. Naval War College. He was a Surface Warfare Officer in the U S Navy for 22 years serving in a variety of destroyer class ships. Since retirement he has been engaged in marketing and business development activities for several high tech and Fortune 500 companies.。