Directory of U.S. Military Rockets and Missiles
Appendix 4: Undesignated Vehicles
ERGM
Copyright © 2003-2024 Andreas Parsch

Raytheon ERGM (5" Projectile MK 171)

Around 1994, the U.S. Navy began a program to develop a rocket-assisted, GPS/INS-guided projectile for the MK 45 5-inch gun. The project was eventually named ERGM (Extended Range Guided Munition), and the EMD (Engineering and Manufacturing Development) phase began in July 1996. The development of ERGM was more difficult than expected, difficulties arising e.g. with the guidance system, the projectile's aerodynamic design, the rocket motor, and the new gun barrel. The first two all-up tests of fully guided EX 171 MOD 0 rounds occured only in February and December 2001, respectively, and were both successful.

Designation Note: The ERGM was effectively a ship-launched self-propelled guided missile, and as such could have received an RGM-nnn designation in the guided missile series. However, the U.S. Navy designated the weapon as 5 Inch Rocket Assisted Projectile, MK 171 in its numerical series for gun projectiles. In accordance with the regulations of the MARK/MOD designation system, developmental rounds were designated EX 171.

Image: U.S. Navy (Naval Surface Warfare Center)
EX 171 MOD 0


The ERGM could be fired only from the latest MOD 4 variant of the MK 45 gun. This modification included structural enhancements to handle the higher firing energy of the ERGM, a new gun barrel (62 caliber), and a new control system to safely handle both ERGM and conventional rounds. The solid-propellant rocket motor of the projectile ignited after it had left the barrel. It was stabilized by four (changed to six in the latest design) flip-out tail fins, and at the apogee of the trajectory the four small steering canards were deployed. The GPS-aided inertial navigation system achieved an accuracy of at least 10-20 m (30-60 ft) CEP at maximum range. The ERGM was armed with 72 APAM (Anti-Materiel/Anti-Personnel) submunitions, which are derivatives of the U.S. Army's XM80 DPICM (Dual-Purpose Improved Conventional Munition) bomblets. The submunitions were designated EX 1 by the Navy (presumably to be changed to MK 1 once the weapon entered service). The EX 1 bomblets were dispensed over the target in a circular pattern of a predetermined diameter between 40 and 100 m.

Photo: Raytheon
EX 171 MOD 0


In March 2003, the first successful test of an ERGM variant with a unitary warhead occurred. At that time, the anticipated time-frame for service introduction of the MK 171 projectile was early 2005, at least three years later than originally planned. However, after further delays due to multiple failed tests, and a significant increase in unit costs, the ERGM program was offically cancelled by the Navy in early 2008.

Specifications

Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!

Data for 5" Projectile, EX 171 MOD 0:

Length1.55 m (5 ft 1 in)
Diameter12.7 cm (5 in)
Weight50 kg (110 lb)
Speed> 3000 km/h (1860 mph)
Range110 km (60 nm)
PropulsionSolid-propellant rocket
Warhead72 DPICM submunitions (EX 1)

Main Sources

[1] Naval Weapons of the World: 5"/62 (12.7 cm) Mark 45 Mod 4
[2] Raytheon Co. Website
[3] "Vision... Presence... Power, A Program Guide to The U.S. Navy", 2002 Edition
[4] Wikipedia: Extended Range Guided Munition


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Last Updated: 23 January 2024