C-RAM Test Video and some history
I've posted before about Counter-Rocket, Artillery, Mortar systems (and I supported the Army's Land-based Phalanx C-RAM system in a previous life). Here's some video of the land-based Phalanx firing:
Gizmodo has an article up with a bit of C-RAM's history -- it's a good, short read. In the comments, a commenter hawkeye18 provided some feedback on using the system:
See my post above for more info on the gun, but the round cylinder thing is what houses the radars. The search radar, which sits at the very top of the dome, looks like a smaller version of the FURUNO units you see on boats, except with two arms facing opposing directions. It spins constantly, scanning a large dome around the unit.
The track radar looks a lot like a height-finding radar (do a google image search to see what they look like), and sits at the front of the cylindrical part. It has a very narrow detection range, but is incredibly sensitive. Once the search radar detects a potential target, it will pass it to the track radar. The gun does not move when it is searching for targets, but when the track radar wants to look at something, it will take the gun with it. In the videos, you can see the mount stuttering around quite a bit before it fires. This is the track radar attempting to get an accurate fix on distance, height, trajectory and speed information. Once it establishes a positive lock, it fires.
The ammo I talk about above - HEIT-SD rounds. Google them, they're quite cool! Here is a picture of them loaded in the gun.
and
Our unit's shoot-down rate was 100% while we were in theater. Everything we actually shot at, we hit. That's not to say that there weren't any mortars or rockets that landed - plenty did, but most of those hit in unpopulated areas, and didn't pass through any guns' defended zones (those two facts are related). Some of them were shot too low and didn't give the gun enough time. Actually, that's not true. The gun had plenty of time, but the humans didn't have enough time. A big, big, big deal in deciding whether to shoot at something or not is positive identification. We have to be absolutely, positively motherfucking sure it's a mortar that we're shooting at. We also have to make absolutely, positively motherfucking sure that there are no other aircraft in the area. If there are, even close, we can't shoot. We call it an airspace foul. It sucks, but shooting down one of our own Blackhawks would be eleventy billion times worse than letting a mortar hit a patch of dirt, or more frequently the lakes surrounding Al-Faw palace. They liked aiming for that. Their aim sucked.
My bit of support for C-RAM was the 20mm x 102mm M940 MPT-SD (multi-purpose tracer w/self-destruct) ammunition C-RAM used -- which unlike the tungsten saboted primary ammo used by sea-based CIWS, is a semi-armor-piercing high explosive incendiary with tracer that has a self-destruct feature. M940 was originally developed as a lower drag, longer-ranged round for the product-improved Vulcan air defense system, but as the Vulcan was retired before M940 was fielded the Army sold the lots of M940 it produced to Israel, who was still using the guns. When C-RAM started we had to buy a bunch of M940 back from Israel until we could get production started. There are other types of HEI 20mm, used in aircraft (like the Navy PGU-28), but they lack the longer range of M940 as well as the self-destruct feature needed for use from the ground. We eventually got production rates up significantly for M940 to support both test and theater requirements.
The round has a pyrotechnic initiation system in its nose, licensed from Nammo-Raufoss, rather than a mechanical fuze. The tracer burns for several thousand meters, and when it reaches the end of the burn it ignites the HE fill causing the self-destruct.
Why 20mm? It was cheap and available, since the CIWS could be adopted quickly and had the requried accuracy and rate of fire. A 20mm was about the smallest round to be able to penetrate the target with sufficient explosive to detonate it -- big mortar rounds and artillery shells are pretty hard targets, while rockets and missiles are "soft" targets. A little bigger payload would actually have been better. We did some later experimentation with 35/50mm ammo and twin 35mm Bushmaster III cannon for a follow-on to C-RAM called EAPS (Extended Area Protection System). EAPS actually had maneuvering rounds that released a frag cloud to destroy the target (more effective against missiles, not as good against artillery), but it was horrifically expensive compared to 20mm. It's a really tough problem, hitting a bullet with a bullet in a very short intercept window, particularly with a man in the loop.
An interesting story about M940 self-destruct and C-RAM: When the first batteries went up at Camp Victory, the crews operating the guns assumed "self-destruct" meant that the rounds turned into confetti and just floated down. The rounds do come apart, but the pieces are up to the size of a quarter and as much as twice as massive. C-RAM has to do periodic alignment fires to align all the radars with the guns. When the guys at Victory did the first alignment fire, they pointed it in what they thought was a generally safe direction (ignoring the surface danger zone diagram they'd been provided) and let fly ... only to rain down shrapnel through the roof of the mess hall, a storage area, and other occuiped areas where the frags went through the roofs of metal containers. We got a panicked call ... "Why are pieces FALLING FROM THE SKY!!!??" ... and after explaining that nothing not fired into orbit stays in the sky once fired up there, we did some calculations and provided a zone in which most of the debris would land. They could then use that for safe alignment fires, though the word would have to get out for soldiers in the line of an actual intercept to take cover, since only 1 round of a 200-300 round burst would hit the target, and the target and the rest of the debris from the intercept rounds had to come down somewhere.
Anyway, once sorted out the systems became pretty effective. We were working on bringing some intercept batteries into Afghanistan when I was there, but I don't know if those batteries were ever shifted from Iraq. Of course, the Army's working on son-of-C-RAM now, aka the IFPC or Indirect Fire Protection Capability, which could be a missile- or gun-based system.
