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MK 45 5-inch / 54-caliber (lightweight) gun
MK 45 5-inch / 62-caliber (MOD 4 ERGM) gun

The 5"/54 MK 45 Light Weight Gun Mount (LWGM), firing a 5-inch shell [approximately 127mm in diameter], is the Navy's primary anti-surface gun battery, and Naval Gun Fire Support (NGFS) weapon. When a target is within the engagement envelope, the 5" gun is significantly more economical than a guided weapon. Versatile and extremely accurate, the gun is also used in an anti-air defense in depth capacity.

The 54-caliber (Mk 45) lightweight gun provides surface combatants accurate naval gunfire against fast, highly maneuverable surface targets, air threats and shore targets during amphibious operations. This lightweight gun system offers significant improvements in reliability and maintainability over the 54-caliber Mk 42 gun systems. The Mk 45 is controlled by either the Mk 86 Gun Fire Control System or the Mk 160 Gun Computing System. Range is more than 13 nautical miles and can fire 16-20 rounds per minute. Each magazine has a capacity of 475-500 rounds. The Mark 45 has been in service since 1971 witht the US Navy and Coast Guard.

The Naval Surface Fire Support (NSFS) program was developed in response to the Navy's Forward From the Sea strategy and the Marine Corps' Operational Maneuver From the Sea doctrine. Both of these documents described the need for a combination of various NSFS systems for close-in and over the horizon (OTH) amphibious operations with sufficient range, accuracy, and lethality to meet the wide range of requirements for the support of assaulting forces during all phases of the operation. The NSFS mission is not only for Naval Gunfire Support but also for suppression and destruction of hostile antiship weapons and air defense systems.

Mk 45 Mod 4 Gun system

The two key elements of the NSFS program are the Extended Range Guided Munition EX 171 and the modified MK 45 MOD 4 gun mount. In conjunction with an increase in barrel length from 54 to 62 calibers and other gun modifications by United Defense, ERGM is expected to boost the 5-inch gun's range from 13 to 63 nautical miles. Due to the development of the EX 171, the existing 5" MK 45 mounts must be modified to support the new round. The EX 171 will be able to operate at greater ranges than existing 5" ammunition. Both elements are in their early phases of development.

The Mk 45 Mod 4 Gun system will enhance Naval Surface Fire Support capabilities and provide fire mission flexibility for anti-surface and anti-air warfare. The 5-inch (127 mm) 62 caliber Mk 45 Mod 4 gun incorporates structural improvements to accommodate higher energies required to fire the new Extended-Range Guided Munition (ERGM). In addition to firing ERGM rounds, the Mk 45 Mod 4 gun retains the capability to load and fire the current inventory of conventional 5-inch ballistic ammunition and provides a platform for firing other munitions technology initiatives such as Cargo Round, Best Buy, and Barrage Round. Other modifications include a longer 62-caliber barrel, an Ammunition Recognition System, a Gun/ERGM interface and a new digital control system. Improvements in the ammunition magazine associated with the new Mk 45 Mod 4 gun have also been developed to facilitate stowage of the larger ERGM rounds and assist shipboard ammunition handling personnel with handling and loading the gun. The Mk 45 Mod 4 gun will be installed in Arleigh Burke-class Aegis destroyers (DDGs 81-108) and in Ticonderoga-glass Aegis cruisers (CGs 52-73) as part of the Cruiser Conversion Program.

Milestone I/II was reached in January 1996, allowing the Mk45 Mod 4 Gun to enter EMD. The Navy awarded the Mk45 Mod 4 gun design and development contract on 5 February 1996. Three Mk 45 Mod 4 kits were produced to facilitate development and testing. The first kit was installed in a proof of concept gun, which successfully completed testing in July 1997 at the Naval Surface Warfare Center, Dahlgren (NSWC/DD), Virginia. The second kit was installed in a government-furnished Mk 45 mount and began Land-Based Testing in August 1998 at NSWC/DD. The third kit was installed in a new Mk 45 gun that was shipped to Bath Iron Works in June 1999 and installed in the Winston Churchill (DDG-81) in November 1999. Four additional gun mounts have been installed in DDGs 82-85. All critical exit criteria associated with land-based testing were met allowing for LRIP approval on 12 April 1999 of the first 17 guns.

The 5"/62 MK 45 modification improves the current 5"/54 gun to handle, load and fire the EX-171 ERGM. Modifications will include structural improvements to accommodate higher firing energy (18 vs. 10 megajoules) associated with ERGM. Additionally, the gun mount modification will include a new 62-caliber barrel, an Ammunition Recognition System, a Gun/ERGM interface, and a new control system.

The Ammunition Recognition System will identify ERGM projectiles and propelling charges and preclude the unsafe mixing of ERGM and conventional ammunition. A Gun/ERGM interface will provide for the transmission of pre-flight data into the guidance and navigation subsystems of the ERGM prior to loading and firing. The control system will be modified to accommodate ERGM changes and to digitally interface with the MK 160 Gun Computer System.

The Naval Surface Fire Support (NSFS) program at Indian Head Division of the Naval Surface Warfare Center has designed/developed a Proof of Concept (POC) propelling charge capable of launching a Extended Range Guided Munition (ERGM) from a 5-inch 62-caliber gun. The NSFS program was born from the Navy's "From the Sea" maritime strategy and the Marine Corps' "Operational Maneuver From the Sea" doctrine. As directed by the CNO Executive Board (CEB), a modification to the existing 5"/54 Mk 45 gun system was determined to be the best alternative to meet the near term needs. The modification included upgrading of the 5"/54 gun system to a 5"/62, design/development of an ERGM and the design/development of a high energy propelling charge.

Based on the current propelling charge performance, it was apparent that the Navy did not have a propelling charge that could be transitioned into a high performance charge. Navy senior propellant technologists, utilizing their extensive knowledge gained through the development of M43 propellant for the Army, suggested that a nitramine propellant would be the key to the goal. Pilot plant and production engineers were soon manufacturing what has evolved into a nitramine propellant. Introduction of a nitramine propellant required engineers to design a new bayonet-type primer specifically optimized for use with the propellant. This task was soon accomplished, and the new propellant and primer were married into the EX 167 propelling charge. The EX 167 has been gun tested and has shown that it is capable of launching ERGM-type projectiles from a 5-inch 62-caliber gun while staying below the gun operating pressure.

Raytheon TI Systems' EX-171 ERGM is a rocket-assisted 5" projectile that will be fired from the 5"/62 MK 45 Mod 4 Gun Mount. It incorporates a rocket motor and internal Global Positioning System (GPS) coupled with an Inertial Navigation System (INS). The coupled GPS/INS will provide autonomous guidance and control to a fixed target location determined prior to firing. The rocket motor will provide range capability far in excess of current ballistic projectiles (Threshold range - 41 NM; Objective range - 63 NM).

The initial warhead configuration for ERGM will consist of 72 EX-1 submunitions per round. The EX-1 is a variant of the U.S. Army-developed M80 Dual-Purpose Improved Conventional Munition (DPICM), which incorporates a shaped charge and an enhanced fragmentation case for use against material and personnel targets. The ERGM's submunitions will be uniformly dispensed within a pre-determined area that depends upon the specific target to be attacked and the altitude at which the submunitions are released. The warhead will scatter the submunition payload over a selectable 20-100 meter area with 10-20 meter accuracy, thanks to GPS-aided guidance.

The combination of the extended range and GPS/INS position accuracy will provide significantly improved performance to meet NSFS mission requirements. A planned Improvement Program (P3I) is underway that will explore ways to expand ERGM's capabilities and reduce its cost. Beginning in 2002, about 50 Aegis cruisers and destroyers will be outfitted with the 5-inch/62-caliber ERGM capability.

Since the ERGM contract award in September 1996 Raytheon, the prime ERGM contractor, has experienced numerous technical challenges in ERGM development. As a result of the technical challenges encountered to date and the relocation of the guided munition development programs to Tucson, the Initial Operational Capability of ERGM has slipped to FY04, and there have been associated increases in development costs. Both the Navy and Raytheon have aggressively tackled these challenges. The ERGM team is working closely with the gun experts at United Defense (UDLP) and NSWC Dahlgren Division (NSWC DD), and, by applying sound engineering principles, they have begun to turn the corner on some of the technical challenges they are facing.

The extended ERGM Team includes Alliant TechSystems (rocket motor); General Dynamics (control actuation system, warhead); L3-IEC (GPS); American Nucleonics (anti-jam circuitry); BAE Systems (inertial measurement unit); and Enser (flight battery).

The Rocket Motor Igniter, which must ignite the rocket motor at precisely the right moment, failed during early testing at the Yuma Proving Grounds. The new redesign has undergone multiple tests and appears sound. A critical new design in gun projectile technology, the Mid-body Obturator not only seals the gun gases to propel the round out of the barrel, but also must de-spin the fin-stabilized round. Raytheon Systems Corporation, United Defense Limited Partnership, and Naval Surface Warfare Warfare Center Dahlgren, Va worked together to overcome the problem. The Ram Brake must stop the round at precisely the right spot in the breach under all conditions of gun wear and over a wide range of temperatures. Tests indicate that the Raytheon Systems Corporation design is satisfactory.

The preliminary Tailfin Assembly design, toughened to survive the 12,000 G's of gun launch, produced too much drag and severely restricted the range. The redesigned fins were subsequently validated in wind tunnel tests. The fins were flight tested and the design appears to work properly. Raytheon has implemented several risk mitigation efforts, including pursuit of alternative guidance system venders. Raytheon recently achieved several successes in their ERGM development test efforts, including a series of rocket motor test flights and two gun-fired canister tests of guidance electronics components. These successes, coupled with new management and their self-initiated risk mitigation efforts, highlight Raytheon's commitment to successfully complete ERGM development.

When ERGM technical challenges surfaced in early 1999, Navy leadership reviewed the ERGM program and requested an independent assessment by MIT Lincoln Labs. Their assessment, completed in August 1999, was that Raytheon and the Government underestimated the ERGM development complexity. They concluded that ERGM development is blazing a new technology trail and problems are to be expected.

The Extended Range Guided Munition (ERGM) conducted a successful flight test on June 25 at White Sands Missile Range, White Sands, NM. The Naval Sea Systems Command's Naval Surface Fire Support Program Office performed the test, the first guided flight that tested the ERGM round's performance at full speed. The test, designated Guided Gunfire-1 (GG-1), met all objectives including canard deployment, rocket motor operation, telemetry function, and Global Positioning System (GPS) acquisition and track.

A significant achievement beyond last December's successful Control Test Vehicle (CTV-2) flight test was the operation of the round at the tactical gun-launch acceleration of 10,100 g's. The December test was conducted at approximately 5500 g's. Post-test review of in-flight telemetry data verified proper operation of all flight control systems.

The June test was the successful culmination of a series of subsystem level tests that demonstrate significant progress toward the 2006 Initial Operational Capability of ERGM. This was the last major all-up round test event prior to the start of the Land-Based Flight Test series beginning in FY03.



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