The Israeli Air Force has again demonstrated why it has few peers in aerial combat. On Monday, an IAF fighter shot down a Hizballah drone that was packed with explosives, and apparently enroute to an Israeli city, perhaps Tel Aviv. Israeli media reports indicate that the drone was over Israeli coastal waters at the time of the intercept; the drone--probably an Iranian Mojaher-class UAV--was detected crossing the border from Lebabnon and was tracked by the IAF until it was knocked out of the sky.
As we've noted in the past, shooting down a UAV is no mean feat. Drones are typically small in size, with a minimal radar return, making them difficult to acquire and track with radar. Additionally, many UAVs cruise at slow speeds--often slower than many helicopters, which further compounds the tracking and intercept problems. Target engagement radars (like those on fighters, or associated with surface-to-air missiles) often look for changes in doppler shift to pinpoint hostile threats. In some cases, the UAV simply flies too slow to be detected by engagement radars; adjusting the radar's "doppler gate" may help a bit, but that also introduces more clutter into the display, making it difficult to spot the UAV.
And, if that weren't enough, the small size of a UAV or drone makes them difficult to acquire visually. During the days of no-fly zone enforcement over Iraq, attempts by Saddam's air force to engage U.S. Predators were usually good for a laugh on a slow day. More often that not, Iraqi radar operators could never find the target; on the rare occasions when they could, the fighter pilots under their direction failed to complete the intercept. Even at close quarters, it was extremely difficult for the Iraqi MiG driver to maintain visual track on an American UAV.
Shooting down a UAV with a fighter is equally problematic. Without radar tracking, more advanced missiles (such as the U.S. made AIM-120 AMRAAM) are largely useless. Infra-red air-to-air missiles (such as our own Sidewinder) may be a better choice, but only if you can acquire the target, l0ck onto the UAV, and maintain that lock. UAVs have a small IR signature, and that problem is compounded by "other" elements (such as clouds) that reflect IR energy, and may cause the missile to break lock. If all else fails, pilots can attempt a gun pass, but that's easier said that done, given the speed of the fighter, the much slower velocity of the UAV, intercept geometry, and the limited rounds available (a "fully loaded" F-16 has less than 1,000 rounds of 20 mm ammunition for its on-board cannon, enough for about 3-4 seconds of burst time. If you're going to use the gun, make the first shot count--you probably won't get another one.
But a skilled IAF pilot made his shot count on Monday, knocking down the UAV before it could deliver death and destruction to an Israeli city. So far, the IAF hasn't provided a lot of details about how it was able to successfully track and engage the drone--and with good reason. Before the current conflict, Hizballah had twice embarassed the IAF, flying UAVs over Israeli territory on two occasions, with no response from the Israelis. The IAF has clearly been working on the UAV problem in recent months, and those efforts paid off on Monday. Hizballah's attempt to score a major political and propaganda victory wound up on the bottom of the ocean.
I've only seen a video clip of the intercept, which was apparently sanitized by Israeli censors. If I had to guess--and it's only a guess--I'd say that the Israelis used a variety of measures to handle the drone threat. IAF UAVs may have provided initial indications of the operation, along with SIGINT platforms. Once the UAV was detected, an IAF AEW or AWACS platform likely vectored fighters to the area; the drone's over-water flight path probably aided in its detection and tracking, eliminating much of the clutter associated with overland radar coverage.
As for what knocked down the UAV, my choice would be an Israeli Python-5 IR missile. The Python-5 is the most advanced IR air-to-air missile in the world, with an advanced seeker and outstanding maneuverability. More importantly, the Israelis use the Python-5 with a helmet-mounted sight; the pilot has a sighting reticle in front of his eye that "slews" the missile seeker to whatever he's looking at outside the cockpit. As long as he could maintain visual on the missile--tough, but not impossible, the Python-5 could see the target as well. After launch, the missile honed on the UAV's heat sources, and knocked it from the sky.
One final note: MSM accounts have emphasized Hizballah's past use of UAVs in gathering intelligence. There are a couple of problems with that scenario, particularly in context of Monday's shootdown. First of all, use of the UAV to provide real-time intelligence requires the use of datalinks and ground support stations, which can provide tipoffs to the Israelis, and allow them to target Hizballah C2 centers more effectively. Secondly, the inaccuracy of the terrorists's weapons of choice (Katyusha rockets) makes targeting support unnecessary and ineffective. "Precision" information is of little value for an area weapon like the Katyusha. Additionally, Hizballah lacks the UAV infrastrucure and operational experience to take full advantage of such systems; as a result, UAV flights will remain a rarity in this conflict, and reserved for Hizballah efforts to strike deep against "untouchable" Israeli targets.