Directory of U.S. Military Rockets and Missiles
Appendix 4: Undesignated Vehicles
Copyright © 2003 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 is 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 are designated EX 171.

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

The ERGM can be fired only from the latest MOD 4 variant of the MK 45 gun. This modification includes 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 ignites after it has left the barrel. It is 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 are deployed. The GPS-aided inertial navigation system achieves an accuracy of at least 10-20 m (30-60 ft) CEP at maximum range. The ERGM is 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 are designated EX 1 by the Navy (presumably to be changed to MK 1 once the weapon enters service). The EX 1 bomblets are 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. The currently anticipated time-frame for service introduction of the MK 171 projectile is early 2005, at least three years later than originally planned.


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

Back to Directory of U.S. Military Rockets and Missiles, Appendix 4

Last Updated: 22 October 2003