Recently, the missile defense-related issue I have been asked about most frequently (my dentist asked me a few days ago) is the effectiveness of Israel’s Iron Dome system against short range rockets launched from the Gaza Strip into southern Israel. Many recent press reports have cited engagement success rates as high as 90%, while other reports are as low as about 75%.  My preliminary assessment based on the public literature (largely newspapers, which are often contradictory) is that that success rate is about 75%. I will update this assessment as I come across more information.

(Image source: http://www.rafael.co.il/marketing/SIP_STORAGE/FILES/6/946.pdf)

The standard operating procedure for Iron Dome is to fire two interceptors in each engagement, although it is unclear if that was the case in the first round of engagements.  Each interceptor costs about $50,000.  The success rate we are interested in is thus the fraction of rockets that that Iron Dome attempts to intercept that it actually destroys, not the success rate of a single interceptor. 

The first Iron Dome battery (a typical battery includes a radar and three launchers, each holding 20 Tamir interceptors) was deployed on March 27, 2011 near Beersheba, the largest city in Israel’s Negev Desert and about 40 km from the Gaza strip.[1]  Prior to deployment, the system reportedly had a 100% success rate in tests.[2]

By the time the system was first used, a second battery had been deployed near Ashqelon (somewhat more than 10 km north of the Gaza strip), and Iron Dome’s first successful intercept occurred here on April 7 against a Grad 122 mm rocket.[3]  Over the next few days, a total of 9 or 10 engagements took place (including the first one), of which 8 were successful.

The second round of engagements took place in late August 2011.  About 130 rockets, mostly Grads and Qassams were fired from Gaza.[4]  Only 27 were assessed as threatening. 

The Jerusalem Post later reported 22 of 28 rockets engaged were successfully intercepted.[5] This is consistent with official’s statements shortly after the attack that Iron Dome had been 78% effective during the August attacks.[6]  Most of the failures were attributed to operator error although some were said to be caused by malfunctions of the interceptor missile.[7]

The third Iron Dome battery was deployed on August 31, 2011 near Ashdod, further north up the coast from Ashqelon.[8]

The final Iron Dome engagements of 2011 took place in late October.  All three Iron Dome batteries were involved in engagements.  However, out of a total of 9 engagements, only three were successful.[9]  The low success rate was attributed to a radar problem, which has since reportedly been fixed.[10]

Thus for all of 2011, we have approximately:[11]

April:               8 out 10   (= 80%)

August:           22 out of 28 (= 79%)

October:          3 out 9 (= 33%)

Total:               33 out of 47 (= 70%)

Almost all of the 2012 numerical discussions of Iron Dome effectiveness attribute to it an effectiveness of 75% in 2011.  This appears to be slightly too high based on the numbers I have been able to find.

The largest episode of Iron Dome usage occurred from about March 9 to March 15, 2012.  According to Pentagon Press Secretary George Little, “When nearly 300 rockets and mortars were fired at southern Israel, Iron Dome intercepted over 80 percent of the targets it engaged, saving many civilian lives.”[12]

The most detailed numerical discussion of the March 2012 attack I have been able to find is the following:

“Of the 250 or so rockets and mortars fired at Israel from Gaza, 166 entered Israel’s airspace, officials said.  Of those, 74 would have struck civilian areas or buildings.  The Iron Dome system intercepted 56 before they could land, a success rate of 75 percent.  Israeli official argue that the Iron Dome also identified rockets that were headed for open areas, such as fields, and let them land.  Factoring those in, Israeli military officials argue that only 18 of the 166 landed anywhere on target, giving the system a success rate of nearly 90 percent.”[13]

This statement makes clear that the often-cited figure of 90% applies to the March 2012 attacks and is not actually the effectiveness of Iron Dome.  Rather it is simply the fraction of rockets that enter Israel’s airspace that either are successfully intercepted or fall outside Iron Dome’s defended areas.

This account is generally consistent with other reports that Iron Dome intercepted about 50 or 60 rockets during the March attacks, or that in total it had intercepted about 90 rockets.[14]

A fifth round of Iron Dome operations took place in around the middle of June 2012, when 7 successful intercepts were reported.[15]  I have not seen any reports of how many engagements were actually attempted, although apparently at least 150 rockets were fired.

In July, Israel deployed an Iron Dome battery near Eilat, on the Red Sea.[16]  It is unclear (to me) if this is a fourth battery or a redeployment of one of the first three batteries, as the deployment was described as a routine rotation.

Overall assessment:  Iron Dome appears to be about 75% effective against the rockets launched from the Gaza Strip.