Tales From The Shop: M247 Sergeant York

I have a deep love in my heart for the 1980’s (duh). Likewise I have an unhealthy obsession with Westinghouse Electronic Systems Group. I don’t know for sure why. Maybe it has something to do with my current employer. For those of you who don’t already know, Westinghouse was an MAJOR defense contractor specializing in radar. They’ve got some big hits, like the E-3 radar, the F-22 radar, and the F-16 radar. But they weren’t all winners. Nothing could demonstrate this more than my look of pure terror and horror when one of my favorite engineers to work with told me he knew people who worked on the M247 Sergeant York.

Credit: Defense Media Network

So for a little bit of context: in 1963 the US Army was looking for a replacement for the M42 Duster, which was a self propelled anti aircraft gun. The M42 thrived in low altitude, short range targets, and was largely there to supplement the Hawk Missile system. By this point, the Army had decided that anti aircraft guns were no longer viable in the jet age, and the M42 was on it’s way out. It had a bit of a messy replacement process though, which resulted in two stopgap systems: The M163 VADS and the MIM-72 Chaparral.

If you ever ran a cargo run to Rota in DPTST3, not the Airport but the Plateau FOB, you’ve probably seen this combo at work. The M163 Vulcan Air Defense System, was effectively a M61 Vulcan atop an M113 with an optical fire control system. Now if you don’t see the issue with that, hi Mike Sparks, hope you’re enjoying the blog. A fast gun on an APC does not an air defense network make. it’s highly going to be, by it’s nature, very inaccurate. US and Israel ultimately, rarely used it for air defense, and instead used it for ground support, although Israel does have several jet kills on it’s record with the VADS. Note: When you check my sources, you’ll see that the M163 DOES have a radar, but it’s range finding only for the gunsight. IT CAN HOWEVER TRACK SPEED AND RANGE. I think that’s incredibly important for accuracy’s sake.

I swear we’re getting to the M247, hang with me. The MIM-72 Chaparral was kind of like the VADS. It was an AIM-9 Launcher on top of a M113 Chassis. Hello again, Mr. Sparks. The problem here is that outside of directly behind an target, the AIM-9 is hopeless, not that it was designed to do anything else. It is after all, a rear aspect missile. I do however doubt that statement, because TM 9-1425-1585-10-1 appears to argue it can work head on. In total fairness to the MIM-72 it was a stop gap meant for a low tier of US air defense, and as such

Now it’s time for the main course, the M247. The Sergeant York was supposed to replace these stop gaps. It was however, VERY RUSHED. The Army wanted the M247 to be built with off the shelf components, and Ford was happy to oblige. This is where Westinghouse comes in. Westinghouse Electronic Systems Group designed the AN/APG-66 Radar which was designed for the F-16, and what a gorgeous radar it was. We’re talking wire wrap backplanes, yellow-brown PCBs, D connectors. It’s an work of art. Something to note though, is it’s a fighter radar. Ergo, an airborne fire control radar, and designed for that purpose.

Credit: Westinghouse Electronic Systems Group

The AN/APG-66 has a toxic relationship with ground clutter. Phase Noise and signal spurs are always a bitch to troubleshoot, ground clutter is a manifestation of that, where basically the target return can’t beat out the overall signal. Well obviously, you don’t want a radar locking on to a tree, so you generally want the radar to ignore a certain noise floor level, and what that is varies from radar to radar. Now, an Airborne radar *Theoretically* won’t have a super hard time with ground clutter, because you don’t see a lot of trees at 25000ft ASL. An Ground based radar on the other hand is literally going to have to deal with everything under the sun, so you’ll have to work around that when you design the radar.

Credit: Westinghouse Electronic Systems Group

Oh wait, they’re not designing a new radar? They’re just using the AN/APG-66? Well fuck. Yes ladies and Generals, the DIVAD Radar does indeed get it’s guts from the F-16, and that’s actually a bad thing. Right off the bat, the radar experienced issues with ground clutter. The gun barrels when pointed directly upward would interfere with the radar’s line of sight, and against high-speed targets the M247 would take somewhere in the range of 10-20 seconds to react. This wasn’t exactly the cardinal sin that got the M247 axed. It’s been a few years since I went through basic firearm training but I distinctly remember “Never point your weapon at something you don’t intend to shoot”

In February 1982 some US and British officers were invited to a lovely demonstration at Fort Bliss. DIVAD was the star of the show and would finally have a chance to show the world’s militaries that they were wrong about it. The time came for the test and the M247 let the intrusive thoughts win, and immediately swung around to aim directly at the viewing stands. I bet that wasn’t a great look. I mean, it probably wasn’t loaded. I think it wasn’t loaded. They wouldn’t load it yet, right? From what I understand, there was a fan on an outhouse, that was perfectly matching the rotation of a helicopter blade, and the M247 locked onto that. Thank God they don’t have outhouses in central Europe. After technicians resolved the issue, the M247 then proceeded to atomize the ground 300ft in front of the target. The M247 didn’t really hit anything during the demonstration, but the Ford Program manager could explain everything. They had washed the M247 the night before, which had fowled up the electronics. This prompted a reporter to ask if it ever rained in central Europe.

There was another round of tests, but it didn’t improve anything. The Sergeant York was all but dead and in 1985 the program was killed. Today one stands outside the State Historic Park in Tennessee. From what I’m told, some of the engineers were transitioned to the terrain following radar for the F-111 after that.

Spaceman’s Take:

I think the M247 is a pretty good example of defense procurement without thought. The AN/APG-66 radar is clearly a good radar and derivatives of it are seen today in really cool applications. It reeks of that reformer attitude of “Why build a new one where there’s this perfectly good one here?” without any thought as to why the old one works at it’s job. At the end of the day, the M247 should have been reworked, and another radar selected, but it wasn’t. The cheapest route isn’t always the right one with these things. Ah but what do I know. I just work on radars for a living.

Sources:

TM 9-1425-1585-10-1 Improved Chaparral System, Department of the Army

TM 9-2350-300-10 M163 VADS, Department of the Army

Jane’s Land-Based Air Defense 1992-1993

Armor The Professional Development Bulletin of the Armor Branch PB-17-96-4

Department Of The Army. The Army Lawyer, August. 1988. Periodical. Retrieved from the Library of Congress

P.S Expect blog posts to become less frequent, we’re just building out a small library to start.

P.P.S Post moved to coincide with James’ Birthday. Happy Birthday James.