XM-246

General Dynamics took their experience and fire-control from the popular and widely-deployed Phalanx CIWS and matched it with 35mm cannon. Both Ford and GD submitted models for testing and Ford was ultimately selected as the winner. In the initial competition for the lucrative $4.5 billion contract, two firms emerged as front runners, General Dynamics (XM246) and the Ford (Aerospace) (XM247). The two, each of which had built a prototype DIVAD, held a shoot-off, and this was won hands-down by General Dynamics. According to a Pentagon report, Ford hit half as many targets as the General Dynamics, and the longest range of the Ford hits was only just over half the longest range of the General Dynamics hit (in all, General Dynamics shot down 15 helicopters, Ford only eight). The army, however, decided to opt for Ford.

The DIVAD contest was specifically started due to the problem of helicopters popping over ridges then retreating back behind it. The then current missile systems then were unable to get lock and fire before the helicopter ducked behind the ridge again, and America only had one gun armed SPAA, the 20mm Vulcan armed M163 VADS, which didn’t have enough effective range to counter helicopters.

Entries

There were several entries for the competition. Sperry Rand’s entry used their Vigilante gun firing 35mm Oerlikon ammunition, as used by several other NATO countries. The gun was fed from a magazine holding 1,464 rounds and was mounted in an aluminum turret. Two radars and an IFF system were mounted on top of the turret.

The entry from General Electric used the 30mm GAU-8 Avenger seven-barrel rotary cannon (the same cannon fitted to the A-10 Thunderbolt II aircraft). It had a single radar for both search and tracking, based on the AN/MPQ-49 Forward Area Alerting Radar.

Raytheon entered a system using the turret from the German Gepard anti-aircraft tank. It retained the same twin 35mm Oerlikon KDA cannons as the Gepard, but had a Hollandse radar and an Oerlikon Contraves fire-control computer. Despite being designed to be fitted to a Leopard I, Raytheon demonstrated that the turret could be fitted to an M48 with some modification.

The General Dynamics entry used the same twin cannons as the Raytheon, but mounted them side by side in the middle of a new aluminum turret. They were fed from 600 round magazines and could achieve a combined rate of fire of 1,100 rounds per minute. Radar and fire control were based on the systems used on the Phalanx ship-board CIWS (close-in weapons system). The search radar was mounted on top of the turret, with the tracking radar next to the guns.

Ford Aerospace entered a system using two Bofors 40mm L/70 cannons, mounted in the middle of the turret. Two radars (one search, one tracking) were mounted on booms on top of the turret, allowing them to be folded down for travel. The tracking radar was based on the Westinghouse AN/APG-66 , as fitted to the F-16 fighter. The turret’s armour was proof against small arms fire and artillery splinters, and the vehicle had NBC protection for the crew.

XM-247

The choice of a 40mm gun in the Ford design was the subject of some controversy. Some maintained that Ford chose it because they had a marketing agreement with Bofors, and could therefore make more profit from Bofors guns. On the other hand, FACC had developed a 40mm round with a proximity fuse, and the larger round meant a greater quantity of high explosive. These both led to a higher probability of a kill.

In early 1978, General Dynamics and Ford were given $79 million contracts to produce prototypes, designated the XM246 and XM247 respectively. In 1980, each company delivered two prototypes for testing at Fort Bliss. The tests lasted five months, and it was said that the General Dynamics vehicle had out performed the Ford vehicle consistently in the tests, but the Ford was controversially chosen as the winner in 1981 (there were accusations that the Ford was only chosen due to intense lobbying). Ford were given a fixed-price contract for the completion of development and the initial production run. The vehicle was officially designated the M247 Sergeant York. The contract included an option for the army to buy up to 276 vehicles over three years, and it was expected that the army would buy a total of 618 vehicles.

Why the US just didn’t stick a FlakPanzer Gepard turret on top of an M-60 and called it a day? It was a proven system with common ammo (in Europe where the wars would be fought that needed this kind of system) all you had to worry about was fitting the turret onto a new chassis.

Because all the gun SPAAG systems built in the West were never really used or required, it was presumed (pretty accurately) that should the cold war have kicked off the West would have maintained almost complete air superiority after a short period of conflict. Most war games or tests conducted by Western commanders showed that the USSR’s air force would have been relegated to a defensive role after a few weeks of fighting even under optimistic scenarios.

Helicopter gunships are the issue however they suffer from the key problem that they require complete air superiority before they can be effectively employed, helicopters are complete tank killers but in the conflict of the time that everyone was building for when the F-15/14 rolled out into the West’s arsenal and the first Mig-25 defected NATO knew that it held the advantage in the air by a large margin.

It was one of the reasons the Soviets had so many SPAAG systems covering both guns and missile systems compared to the West as they were aware that they would need them.

On top of that the new systems that were developed such as Gepard and Marksman for the west were primarily aimed towards protecting tanks from low level gunships and attack aircraft such as the SU-25 but by the time they had been developed the Missile had already been cemented in the West as the leading AA weapon to field and the SPAAG system was relegated. It was further driven back by the development of MANPADS systems and light AA vehicles such as the US army’s Avenger.

The technical failure of Sgt. York comes down to Ford Aerospace being way too ambitious.

Their decision to use a modified version of the F-16 Fighting Falcon’s radar as the central component of an all-new fire control system instead of upgrading an existing proven surface-to-air fire control system like Gepard or Phalanx (as pretty much all the competing designs did) was motivated by the desire to put *the* most advanced possible system into competition while at least nominally satisfying the requirement for off-the-shelf components. The Sgt. York’s cannon feed system was similarly cutting-edge; it was a then-revolutionary linkless linear feed allowing pushbutton switching between dual ammunition types, a “killer app” feature that none of the other DIVAD proposals could match with conventional linked feeds.

Unfortunately turning a system designed for air-to-ground around to operate as ground-to-air proved much more difficult in practice than theory, and the very limited timescale allowed for development meant that the very bad teething issues became painfully public. If development had continued, it probably would have worked out in the end; there was nothing INHERENTLY wrong with the setup.

The only actually bad thing about the Sgt. York was that it for reasons of industrial politics (Ford having a pre-existing contract with Bofors), it was equipped with Bofors 40mm L/70 cannons rather than Oerlikon 35mm cannons — the problem being that the long-barrel Bofors is totally incompatible with its predecessor the Bofors 40mm L/60, all the way down to firing completely different ammunition. And said predecessor is the only 40mm that’s actually in U.S. inventory, so Ford’s unfortunately successful lobbying to allow DIVAD to be a “30 to 40mm cannon” instead of the established NATO standard 35mm for heavy AA had the effect of delivering a configuration whose only advantage was increased profits for Ford and Bofors. The XM247 did use the same 35mm Oerlikon cannons.

The reason I say that the best DIVAD decision would be to reject the Ford for the General Dynamics is that DIVAD was pretty much regarded as a we need it yesterday emergency procurement against the emergent threat of more capable attack helicopters like the Hind; that’s really not the time to go pushing the cutting edge the way Ford was trying to sell. Ford’s design certainly has superior long-term potential, but General Dynamics ‘s design is a much lower-risk development which better meets that immediate need.

Computing gunsights were developed precisely because even with something doing the calculations for you, hitting a moving aircraft is extraordinarily difficult on the best of days and a human being using fixed sights (i.e. no computer involved) makes that even worse. Radar is used because it can essentially calculate – with perfect accuracy – the speed, range and altitude of a target and feed that into an aimpoint. Computer-control is used because human reaction times are worse than electro-mechanical reaction times: a good feedback system can keep the barrels on aimpoint better than 99% of the time, for hours at a time.

As an aside, this platform will be absolute murder in an urban environment or against infantry or other vehicles as well. A hail of 20mm shells coupled with a sensitive thermal imager and good optics is a damned scary thing to fly, drive or run into.

The hilarious postscript to the DIVAD story is that the Army gave up and cancelled the system just as it reached the point of finally being debugged enough to actually start working properly. The Navy promptly swooped in and acquired the four Sgt. York prototypes for the cost of shipping them and has actually been using them as opponent systems for pilot training ever since.

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