North Korean Nuclear Weapons as Economy of Force Pt 1: Effect & Cost of Long Range Artillery

Recommended before reading this: If It’s Worth Doing, It’s Worth Doing with Made Up Numbers

North Korea last week offered to remove long range artillery from the DMZ.  But of course: they don’t need it anymore.  They’ve got nuclear weapons.  But what, exactly, is the logic behind replacing the conventional deterrent with a nuclear one?  After all, North Korea’s current deterrent system has worked.

North Korea’s long-range artillery (LRA) has up until now served as both a deterrent and as a deep-strike capability.  The North Koreans have no hope of conducting any meaningful air attacks against South Korean targets during a war, so they emplaced the LRA instead.  The artillery fire would be unobserved, but on the other hand most of the likely targets are static.

LRA represents a considerable investment in manpower and maintenance for the North Koreans.  Their main delivery systems, in order of increasing range and power, are the 170mm “Koksan” gun, the 240mm multiple rocket launcher (MLRS), and the 300mm MLRS.  The 170mm gun can reach the northern parts of Seoul, the 240mm rockets can reach most of Seoul, and the 300mm MLRS can reach down to Daejeon, threatening major installations south of Seoul.

I want to emphasize that this is a hypothetical to create an estimate for both the countervalue damage caused by this force, and give a rough estimate of North Korean investment.  Accurate numbers for the number of these systems in use are not publicly available, if at all.  Estimates are generally around “several hundred” 170mm guns, around two hundred 240mm MLRS, and fewer than a hundred 300mm MLRS.  We’ll assume that all artillery is organized into battalions of 12 pieces each.  We’ll go with 5x 300mm battalions (60 pieces), 15x 240mm battalions (180 pieces), and 40x 170mm battalions (480 pieces).

The Power of Long Range Artillery

Now we try to figure out how much damage these pieces can do.  The Koksan is similar to the American M107 175mm howitzer, which was used in Vietnam.  The M107 fires a ~150lb shell, at a rate of 2/minute, for 120/hr.  The shell is about 50% larger than a 100lb 155/152mm shell, so instead of a 50m casualty radius we will go with a 60m radius (inverse square law in effect).  To further specify, anyone within a 20m radius would be killed, anyone from 20-60m is wounded.  This is for an airburst against a person standing in the open however, not in a heavily built-up urban environment.  Relying mostly on intuition, I will quarter the casualty radius to make up for the natural cover provided by the surroundings and the tendency to seek immediate cover.

Assume the 240mm rocket is similar to the Russian 220mm Uragan, with a 220-lb warhead.  We’ll go with a 30m kill radius and an 70m wound radius in the open, down to 7.5/17.5 with the terrain adjustment.  Each launcher carries 22 rockets, which it can fire quickly, although it then needs to reload, reposition, and retarget.  Perhaps one salvo every 20 minutes, or 22×3 = 66 rounds per hour.

The 300mm rocket is probably similar to the BM-30 Smerch, with a ~500lb warhead.  40m kill radius, 80m wound radius (adjusted to 10/20m).  Each launcher has eight tubes, which it can fire in about a minute, although it takes a while to reload and reposition.  Again, one salvo every 20 minutes, or 8×3 = 24 rounds per hour.

This gives us 57,600 170mm rounds, 11,880 240mm rounds, and 1,440 300mm rounds per hour.  However, that’s an unrealistically high estimate.  Not all of the launchers work, not all of the munitions will explode…and not all of the warheads will contain high explosive.

The museum-piece Koksans might have a 50% readiness rate and a 20% dud rate.  They are now firing 28,800 170mm rounds, of which 23,000 will actually explode.  The newer, better-maintained MLRS might have a 70% readiness rate and a 10% dud rate, giving us about 7,500x 240mm  and 900x 300mm effective rockets per hour.

In an all-out scenario, some of those munitions will be fitted with chemical warheads.  I’ll look at the effects later, but if I had to guess then maybe 10-20% of warheads would be chemical.  Split the difference, call it 15%, and now we have 19,550x shells, 6,375x 220mm rockets, and 765x 300mm rockets exploding.

Since we’re considering this a countervalue strike, especially given the inaccuracy of these weapons, let’s look at Seoul.  Seoul has a very high population density of 17,000 people per square kilometer, or .017 people per square meter.  The 300mm rockets will probably be aimed past Seoul given their range, at relatively less dense targets like airfields and headquarters.  I will use the town of Osan, just south of Seoul, as an exemplar; it has 200,000 people in about a 43 square kilometer area, giving us .0046 people per square meter.

In the first hour:

Total: 44,104 killed, 287,513 wounded

The ratio between wounded and killed looks a bit high to me.  Perhaps it includes relatively minor injuries that wouldn’t require immediate treatment.   A major hidden assumption, also, is uniform distribution of incoming shells: no round lands in the same place, and there isn’t even any overlap between casualty radii. Also, the firing batteries never run out of ammunition.

Once the first barrage lands, anyone in the target area will take cover.  I will model this as a further reduction in the casualty radii by 75%.  Also, counterattacks will begin; I will assume that these will reduce the attacking LRA by 1% per hour.  Summing the resulting series gets another 136,400 dead and 890,000 wounded before the LRA is silenced.

Assuming the 170mm shell is 15% high explosive filler (as is the usual 155mm shell), or 22.5lbs, the total amount of high explosive launched at Seoul is about 70 kilotons.  Keep that in mind!

Total: about 1.3 million casualties (180,500 dead, 1.1 million wounded wounded)

That’s just from high explosives, though.  What about the chemical weapons?

The largest chemical attack so far has been Halabja 1988 in Iraq.  At the time, Halabja looks to have had 70,000 people.  The attack, using a modern cocktail of lethal agents, targeted the city indiscriminately, killing around 3,500-5,000 and injuring about 7,000-10,000.  Halabja had and has a lower population density than Seoul overall, although it’s difficult to determine how much because most figures for the town clearly include sparsely populated surrounding areas.  Also, the high-rise residences common in Seoul would provide some protection against the heavier-than-air chemical agents.

Ignoring the confounding factors, a simple ratio means another 500k-700k dead and 1 million-1.4 million wounded.  Note that this would provoke the use of nuclear weapons by the United States in retaliation.  I am here using an assumption that the munitions discussed above produce a “blanket” that affects the target collectively, rather than trying to determine the effects of each given impact.  I believe this to be the correct approach based on my understanding of chemical warfare.  I’m not that confident in the reliability of this number, but I think it’s a good benchmark.

(It looks like the most lethal effect of the explosives might simply be to drive the population into shelters where they’re killed en masse by chemical agents sinking down.  People might be safer in their high rises; some accounts from the First World War noticed a similar dilemma, with chemicals lingering in trenches.)

The above gives us a total of about a million dead and two or three million wounded, many of whom would die later given the inability to treat so many people.  These three to four million casualties are probably an upper bound on what the North can achieve with its conventional deterrent.  For instance, it assumes no overlap between chemical and explosive casualties, which is silly, in addition to the absurd assumption of uniform distribution of munitions and generally zero overkill.  However, even this worst-case scenario wouldn’t actually annihilate Seoul, much less South Korea.  80% of the population in the target area would survive, and two-thirds would be relatively unscathed.

The Cost

We assumed above that the North Koreans maintains 60 battalions of artillery.  The American units with which I am most familiar have about 500 soldiers in a howitzer battalion and 250 in a rocket battalion.  However, these units are expected to operate with a great deal more independence and mobility than the North Korean units being discussed here.  If there are 200 soldiers in a North Korean LRA battalion, this gives us 12,000 soldiers. These are firing units, however; the total force is probably substantially larger, maybe 50,000.

Then there are the numbers of munitions.  The forces above fired over 1.4 million artillery shells, 420k 220mm rockets, and over 50k 300mm rockets.  Not a single one of these was fired in support of tactical maneuver.  Even assuming minimal costs of $300/shell, $1000/rocket, and $2000/rocket, this is around a billion dollars in munitions, against a GDP of under $30 billion, before even attempting to actually fight anybody.  The point is, it ain’t cheap.  This didn’t even attempt to include the expensive intermediate-range Scud-type missiles in the North, which are probably counterforce weapons, more or less.

Next, I’ll look at what why nuclear weapons might be an attractive replacement for all of this — which is what I originally intended to write about — in a follow-on post.

Edit: After I posted this, I found a much more detailed/competent/professional analysis of this problem by Mr. Roger Cavazos.  I’m encouraged that my first-volley estimate was at least in the ballpark of his more informed method.