81mm mortar used by the Coast Guard during the Vietnam era

It seems technology is making hitting small, fast, maneuverable targets with precision not only easier, but also cheaper.

We have talked before about the possibility of using small guided missiles (Hellfire, Brimstone, Griffin, or 70 mm guided rockets like APKWS) to allow the Coast Guard to engage small, fast, highly maneuverable threats, while minimizing the chances of collateral damage that accompany the use of unguided rounds from machineguns or auto cannon. Now there seems to be another alternative, and it even has a history of use by the Coast Guard, the 81 mm mortar.

Popular Mechanics reports the Marines will be getting a guided 81 mm round called ACERM (Advanced Capability Extended Range Mortar) that will incorporate both a GPS, and potentially more importantly for the Coast Guard, a semi-active laser (SAL) guidance system that should provide a one meter circular error probability (CEP, that is 50% of the rounds will fall within one meter of where the laser is pointed). Additionally the round will have a range of about 18 kM, comparable to that of a 76 or 57 mm gun. Cost per round is expected to be about $10,000. That is more than the China Lake Spike, but range is much greater and the warhead is substantially larger.

The firecontrol computer/programmer is a two pound “Miniature Mission Setter,” in reality a rugged Android tablet.

In addition to the Popular Mechanics post, I also found this power point presentation (pdf) that provides more detail.

The 81 mm mortars the Coast Guard used in the Vietnam era are all gone now, but they were hardly high tech, expensive, or difficult to produce.

Maybe we at least need the laser designator anyway:

Like some of the other systems considered, in addition to the mortar and mortar rounds, to use these effectively, we would need a laser designator. Based on a recent contract award, laser designators cost about $60,000 each.

Laser designators might be a good idea anyway. If we need to call in assistance from the Navy, Marine Corp, or particularly the Air Force or Army (who tend to be clueless about marine targets), one of the issues will be identifying the target, and a laser designator would be a good way to do that. Not only to identify the target, but also to show where we want them hit.

Limitations:

While the potential range of the 81mm mortar round may be over 18,000 yards, for our purposes, its effective range is probably limited by the range of the laser designator which can be further limited by atmospheric conditions like fog, rain, snow, smoke or sand storms (like might be encountered in the Persian Gulf). The Power Point brief does suggest that a small unmanned air system (sUAS) equipped with a designator, might be used to complement (and extend) the system.

Because this is a high angle weapon, with the projectile designed to strike the target in a vertical dive, and because the warhead uses “High Density Pre-Formed Fragments” that would presumably spread out horizontally, it probably would not be particularly effective against medium to large ships. It seems to be intended primarily as an antipersonnel weapon. The danger radius for fragments might even be an issue in some circumstances.

It is still a crew served weapon with the crew highly visible and exposed.

Advantages:

Unlike some missile in a box systems, this looks like a gun. It might have some deterrent value in some circumstances.

Reportedly it makes the 50 cal. mounted piggy back more accurate.

If we were in a situation like Market Time, where patrol boats might incidentally support troops ashore, this might be a good option.

Is it the “best” alternative?:

We have an array of possible systems to address the possibility of a maritime terrorist threats. Hellfire, Brimstone, Griffin, APKWS, the China Lake Spike, this smart 81 mm mortar round. All would probably be effective against smaller targets. None are likely to be fully effective against larger targets.

For the larger threats, I have been suggesting WPCs, and probably WPBs, be equipped with light weight torpedoes or even a variant of the anti-torpedo torpedo, to use as a ship stopper that could home on the target’s propellers,

LRASM might also be an alternative. Coordinating a long range LRASM strike is more complex and probably more expensive than the torpedo alternative. On the other hand, it would bring along with it a new naval wartime capability that would support the Navy’s “Distributed Lethality Initiative.”

We really need a set of capabilities that provide a high probability against any element of a spectrum of threats, because if any one element is not addressed, that is likely the element terrorists will select.