Mortar bombs and countermeasures

Today's mortar bombs are almost all very similar in concept to World War 2 mortar bombs, the greatest differences are the proliferation of cargo (submunitions, cluster, ICM, DPICM) munitions and the streamlining of the body of many mortar bomb types for better aerodynamics. Radio proximity fuzes - a WW2 invention - are now rather normal on high explosive mortar bombs as well.

This is the kind of old school mortar bombs which has spawned multiple countermeasures in the meantime.

The oldest countermeasure is the late 40's invention of counter-mortar radars. These radars still employ the same principle; they search the horizon for contacts (mortar bombs in flight) and then collect further data on the contact's trajectory. A bit mathematical interpolation by a computer later the user knows the approximate origin of the contact.
Mortar teams facing such a sensor are very much impaired in their ability to accomplish their mission. Their effectiveness is badly degraded even if they know and apply all the tricks of the trade, knowing about the radar's limitations.

Another countermeasure are hard-kill defences; autocannons and even lasers (a German 40 kW laser has been successfully tested on mortar bombs, for example). These depend on the radar for fire control data, of course.

HE mortar bombs employ kind-of-radars themselves for fusing at a most 'promising' height over ground. The very first such fuzes were meant for HE grenades fired at aircraft, so as to make a direct hit or difficult time fusing unnecessary. The inventors were huge fans of the approach and claimed it's reliable. Someone else (engineer of physicist, I forgot) was sceptical and his team improvised an effective jammer within two weeks with the benefit of knowing the fuze. Such jammers were not introduced during WW2, but became rare specialised equipment during the Cold War and are now more common; "Shortstop" was and is a famous such tool.

Finally, electromagnetic pulse emitters could be used to counter guidance or electronics-dependent fuze types of mortar bombs.

And this is where countermeasures to the countermeasure come into play:

Proximity fuszes on optical principles have been developed to maturity two decades ago, and more old-fashioned methods such as point detonation super quick fuzes, jumping-back-on-impact mortar bombs and time fuzes (now better thanks to electronics and electronic maps) negate the protection by usual jammers. Cluster munitions were (and are) easily used with time fuzes, since small errors of a few metres don't influence their effect much. The electronics-free approaches are even resistant to microwave-based hard kill defences.

Spin stabilised mortar bombs (such as the French 120 mm of the very much proliferated MO-120 RT mortar) are troublesome for lasers because the laser effectively faces the whole circumference instead of one side only. This is only a problem if the heat capacity of the mortar bomb's shell isn't the limiter, of course. After all, heat disperses quickly in steel.
But what if the mortar bomb is an insensitive munition, with a much higher cook-off temperature than usual? The laser might need too long to reach this temperature.
There's also the possibility of highly reflecting surfaces, which would degrade the laser's effect initially.

But let's not fixate on laser countermeasures. After all, the really troublesome countermeasures appear to depend on the fact that mortar bombs have a tendency to be ballistic projectiles; this enables the interpolation of their origin. Now what if the mortar munition is not a ballistic munition, but rather a guided or course correcting one (sometimes called 'quasiballistic')? It may manoeuvre on autopilot early on and then fake a trajectory which lures counterfire to some unoccupied area.
Manoeuvring munitions also make the hard kill approach much more difficult, albeit the low velocity of mortar bombs (usually less than 280 m/s; subsonic) means that this doesn't nearly help as much the mortar teams as it helps the howitzer teams against hard kill defences.

Finally, why tolerate detection and tracking by radar at all? Even moderate changes of the shape of mortar bombs could reduce their radar cross section by a factor of ten and make detection much less likely at least for the mortar teams which are rather distant from the radar. A polygonal surface would be a cheap approach for radar stealth, albeit it would require some discarding sabot in order to achieve a decent sealing for the propellant gasses in the tube. That's tricky because of the tail fin section. It's still likely practical.

And these were merely the hardware counter-countermeasures. The "tricks of the trade" of the mortar teams are probably still more powerful.

Military tech journals feature high-tech countermeasures occasionally. We shouldn't forget that some of these are (still) impractical, others will rarely face fine conditions for employment and all of them will sooner or later face counter-countermeasures and de-valuing new tactics (tricks of the trade).
I wish there was more written on the potential employment of new tools, not just a presentation of the mere technical performance.
No doubt many, many novelties will disappoint in (hopefully distant) future wars, just as it happened in past wars.




  1. faceting doesn't work well here as most mortar bombs spin to enhance accuracy, (yes, even the finned ones) what you wind up with is scintillation as the RADAR reflectivity changes depending where the reflective surface is in relation to the RADAR. The best bet here is to look to absorptive / transparent materials to reduce hot spots ( like the fin array, it's practically a corner reflector).

    Rifled mortars as currently built would also have to go down the "stealth" RCS reduction, Eliminating metal rotating bands and obdurators (( not a hard option, materials exist)

  2. The mass of the projectile needs to spin for accuracy while the facets need to be in place for defeating radar.
    Take for example this construction:
    A faceted outer hull that doesn't spin within which the heavy bomb spins. It's basically a radar reflection hull put on the usual mortar bomb with fins to stabilize it in non-spinning motion. The spinning effect of the mortar bomb must be achieved by other means than the fins, such as rocket propulsion for the spin.

  3. I looked something up. Here my results (2, 3) and stuff I knew already:

    (1) Modern relatively long mortar bombs can be stabilized well with fins alone and need no spinning.

    (2) Unintentional spinning is caused by a large angle of yaw (~angle of attack for aircraft); near the apogee. This is not the time when typical counter-mortar radars detect mortar bombs; that would be slightly above the horizon - much earlier.

    (3) Unintentional spinning can be reduced by shrouding the fins.

    (4) Same for RCS.

    (5) Keyword "corner reflector"; this matters with 90° angles, but common angles between stabilizer fins on mortar bombs are more like 60° and orientation would be off for the purpose as well. The many edges are more of a problem.

    BTW, to de-couple the main mass and a polygonal shroud would be too elaborate IMO.