Patria and Kongsberg Defence & Aerospace have teamed up for the future U.S. turreted mortar programs.
The news here is simply that the US Army has a program to procure a turreted mortar. I don’t think the US has ever had one, at least not since the 19th century.
They offer some interesting possibilities for arming small naval craft like patrol boats. For our purposes, they are effectively low velocity short range cannon, that can fire a relatively large projectile, while requiring far less of the vessel than a typical higher velocity naval gun.
Looking specifically at the 120mm mortar, it fires a 4.7″ diameter projectile weighing about 30 pounds (I have seen weights quoted from 28 to 31 pounds. Part of the weight would be consumed propelling the projectile since this is both projectile and propellent). That is less than half the weight of a modern 5″ projectile (70 pounds) but about five times the weight of a 57mm projectile, and the Patria turret has been mounted on some very small vessels. It has even been tested at sea in a standard sized 20 foot container.
Unguided mortar rounds tend to be less accurate than typical naval guns, but guided rounds are changing that. The Army is working on a new round.
The HEGM program objective is to create a round accurate to within one meter CEP, with dual GPS/SAL (Semi-Active Laser–Chuck) guidance to hit targets that have relocated and to function in a GPS-degraded environment.
Range is about 8,000 yards, similar to that of the Hellfire or the effective range of the 57mm Mk110 or 76mm Mk75 guns using unguided projectiles. I have seen ranges double that for smart mortar rounds. In any case, it would have sufficient range to fire from outside the effective range of likely improvised armament for a terrorist controlled vessel.
The Coast Guard is not without experience in the use of mortars on patrol boats, having mounted them on 82 foot WPBs as well as other vessels during the Vietnam era.
It is behind the pay wall, but the US Naval Institute Proceedings has a short argument for the Navy to look seriously at adding mortars to Its inventory of weapons. In addition to its use as a weapon, the author contends that they could be used to launch decoys or UAS. He suggests:
“The Navy could take an incremental approach to integrating mortars onto ships:
- “Task the Naval Surface Warfare Center at Indian Head, Maryland, with testing a variety of available mortar rounds for effectiveness against maritime targets, potential for countermeasure launching, and suitability for shipboard use.
- “Encourage the Marine Corps and the Naval Research Lab to pursue an anti-armor version of the ACERM.
- “Fire existing Marine Corps and Army mortars from ships during a SinkEx. Assess their effectiveness on the target and their structural impact on the ship.”
This is not as good an answer to the problem of stopping larger vessels, that might be used in a terror attack, as torpedoes (probably the best solution) or missiles like Hellfire (a good solution against small vessel threats with some capability against larger vessels), but it has some capability and would also make our patrol boats more useful in the support of troops in the littorals against targets on land.