Thursday, July 17, 2014

ISIS now has dozens of US-made howitzers

By Donald Sensing

ISIS Has 52 American Weapons That Could Pummel Cities

ISIS militants may be in a position to pummel other cities in Iraqi army control after capturing American-made weapons the group seized from the Iraqi military, Mitchell Prothero reports for McClatchy DC.

During ISIS's blitz across northern and central Iraq last month, the group captured upwards of 52 155mm M198 howitzers.
An M198, 155mm, towed howitzer being fired by US Army troops.
As a retired Army artillery officer, I can tell you that starting to shoot these things will not necessarily be easy for ISIS. Every howitzer has unique firing tables and ballistic solutions, although calculating those solutions is computationally the same. But unless ISIS also captured the technical ballistic publications for those particular guns, they can fire them, but it will basically be unaimed fire. Nowadays, of course, technical firing data is computed electronically, but inputs have to be done accurately and correctly. GIGO still applies. 

All of this computation is to answer three questions: 
  1. Which direction to point the tube (we call this "deflection")
  2. How high above the ground to point the tube (we call this "quadrant")
  3. How fast should the projectile leave the tube. This varies according to how much propellant is used. Propellant comes in bags encased in a canister. Each canister contains propellant for one round in eight bags. 

There is also a calculation to account for the difference in altitude between the howitzer and the target. This solution is called "site," and techncially consists of site plus angle of site. But angle of site is not actually calculated unless the difference in altitude is +/- 100 meters or more. 

If ISIS has former artillerymen in their ranks, say from Syria or Iraqi Sunnis, then simply shooting the guns will be a lot easier since all modern towed howitzers work much the same and the ballistic principles are quite the same. 

But, as the article goes on to say, for ISIS's purposes accurate fire is not necessary when the target is, after all, the entire city of Baghdad.

The 155mm high-explosive projectile weighs 95 pounds and has a blast radius of 50 meters (55 yards), defined as the radius at which at least half 90 percent of exposed persons will be struck by shell fragments. So it's basically a circle with a slightly larger diameter as a football field. The M198 can, if crewed skillfully, fire two rounds per minute indefinitely.

A correction: the blast radius is the 90-percent kill radius on unwarned (that is, standing) personnel. The casualty radius is the 50-percent line and for the US 155mm projectile is 100 meters. The area of in which at least half  of persons become casualties is thus 31,400 square meters. From one projectile.  

So imagine a section of Baghdad being  residents blasted with 15 minutes of 52 M198s firing two rounds per minute. That's 1,560 rounds. No wonder that residents of Berlin, Germany, said after World War 2 that American and British bombers did not terrify them as much as Soviet artillery did, once it started shelling the city. Bombers came, bombers went. But the artillery was around the clock. It never stopped.

But what we do not know is how much ammunition ISIS also captured. That's the real issue, feeding the beasts. Fifteen minutes of sustained firing, as in my example, uses projectiles weighing 74 tons, plus another 23 tons or so of propellant canisters. Not a casual undertaking.

Here is an example of the kind of technical data I am talking about: Firing Tables

And this PDF os a slide presentation has examples of actual M198 firing tables.

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