Mortar testing a specialty at U.S. Army Yuma Proving Ground

For versatility and power, the humble mortar has been a key indirect fire weapon for generations, and is likely to become even more important as technology makes mortars more accurate and maneuverable. Hard-to-traverse mountain terrain, urban areas, and a rapidly-moving enemy are all situations that call for the mortar as a weapon of choice. In addition to their firepower, American forces commonly rely on mortar teams to fire illumination rounds to light up areas at night or white phosphorous rounds to provide smoke screens that obscure troop movements during daytime operations.

Whether carried by a Solider or attached to a combat vehicle, virtually every type and variant of mortar in the ground combat arsenal goes through rigorous developmental testing at U.S. Army Yuma Proving Ground in southwestern Arizona. The facility also performs acceptance testing on lots of existing mortars on virtually a daily basis.

American forces use mortars in three calibers: 60mm, 81mm, and 120mm. The typical mortar consists of a ballistic tube attached to a base plate by a movable breach ball and propped up by a bipod. The base plate is typically the heaviest component: for a 120 mm mortar, it can weigh over 150 pounds. Mortar projectiles, which ignite when their firing pins hit the bottom of the tube, are propelled by explosive nitrocellulose charges of various sizes attached to the round, with larger charges providing greater distance. Mortars come with sight units for aiming and 60 mm versions can be fired in a hand-held mode.

Testing

As the Department of Defense's second largest installation, YPG's immense size is often a major factor in attracting test customers. Since mortars are capable of ranges only a fraction of the distance of an artillery projectile, there are far more facilities that theoretically could accommodate mortar tests. Though YPG's customers are mostly drawn to its institutional expertise and highly instrumented ranges, the proving ground's sheer size ensures that fired mortar rounds can be safely recovered for study. Its borders also contain a wide variety of terrain that simulate conditions in Southwest Asia, including mountains that are highly coveted in the testing of guided mortars, whose developers are especially keen to challenge these advanced systems with test firing from a low elevation into a higher elevation.

"We never like to turn away customers," said Claudia Anderson, chief of YPG's munitions and weapons division. "We always find a way to work more efficiently and fit people in. Our schedule has expanded to frequent weekend firings."

YPG conducted over 200 unique mortar tests in fiscal year 2011, constituting a majority of the workload for YPG's weapons operations crew and a significant portion of the overall munitions and weapons mission.

"Since 9/11, about two-thirds of our division workload has been mortars," said Wayne Schilders, chief of weapons operations. "That includes tests on the mortars themselves as well as mortar fire in support of tests of radar and counter-mortar technology."

While ammo surveillance tests of mortar rounds look at whether a stored round can still function as intended under normal conditions, developmental tests of new systems or updated components on existing systems seek to improve the range, accuracy and reliability of the weapons, and are pushed to extreme limits.

"We usually test a new item by firing it 10,000 times," said Patty Jonez, a test officer in the munitions and weapons division. "Most mortars in operational units don't fire that many times. That's why we test--to find out at what point it breaks."

This type of testing aims to see whether a mortar conditioned to extremely hot or cold temperatures will still fire. Mortar tubes become extremely hot after continuous firing and a system under development is tested in a similarly scalding tube to ensure the round doesn't 'cook off', or explode in the tube, or in mid-air prior to reaching its target. The mortars are often fired under unusually high pressures, too, to determine the extent of their abilities. The base plate, which will ultimately crack under the strain of repeated firings, always garners intense scrutiny from testers.

The ballistic tubes used by YPG mortar testers are outfitted with holes to accommodate pressure gauges and other instrumentation. For a conventional mortar, YPG testers gather information like chamber pressure and velocities, and measurements of the range and deflection of the projectile's point of impact, which is usually calculated by observers stationed in towers overlooking the test range. For guided mortars, testers also take high speed camera images at both the gun tube and the point of impact, track the round in mid-flight with massive camera mounts, and sometimes even attach telemetry devices to the round itself to measure flight characteristics and assure that it acquires its satellite signal at the proper time. The instrumentation that allows a guided mortar to have this capability must also be relatively small, for mortars need space for their explosive payload.

All of the expensive, specialized instrumentation for this type of evaluation is already in place at YPG as a result of its longstanding status as the premier facility for artillery testing. The artillery mission also means YPG has a deeply experienced staff at its ammunition plant that can assemble complex ignition or propellant charges, and a metrology division that can accurately measure the physical properties of a given projectile, be it a mortar or artillery. Rounds that have been recovered after firing can be dissected at YPG's water jet-cutting facility.

Developmental testers usually want to see how their system can perform when conditioned to temperatures as low as -50 degrees and as high as 145 degrees, and YPG has conditioning chambers to accomplish this all year round. Some tests even call for rounds to be soaked in water prior to firing.

Testers also strive to consider how the rounds will fare under projected threat conditions: will the mortars detonate if a truck they are being transported on is struck by .50 caliber machine gun fire? Will rounds detonate if hit by shrapnel? Knowing what to expect in these types of events is crucial information for troops in the field.

All through these challenging tests, safety is a primary concern. As such, gunners typically do not fire the test projectile by dropping it into the tube as a Soldier in combat would. Instead, most rounds are suspended over the mortar tube with a metal clip attached to the fuse or muzzle, which is pulled away by a long lanyard to fire the round. In the rare instances where a test requires fire that replicates actual use, the gunners, many of whom are uniformed artillery veterans, wear Kevlar vests and helmets.

Mortar testing is a perpetual and cyclical component of YPG's test mission: Its presence in the developmental testing of a given mortar round offers valuable knowledge of the projectile's capabilities throughout its life cycle.

Carriers and Self-Propelled Systems

When American mechanized infantry transitioned into Stryker combat brigades, the mortar came along for the ride with the M1129 Stryker Mortar Carrier. YPG's combat automotive division has tested all variants of the Stryker and the munitions and weapons division worked night and day to ensure the performance of the mortar.

"For the Stryker test, we fired 24,000 rounds on two weapons," Jonez recalled. "We were running two shifts a day to accommodate this."

With a mechanized mortar carrier, the scope of evaluation goes far beyond firing. The repeated shock produced by a 120mm mortar's recoil can adversely impact the vehicle's engine mounts and suspension system, for example. This requires YPG testers to take a holistic view of a system.

"We have to test everything from being able to shoot accurately to ensuring its durability," said Schilders. "We also have to test system ergonomics, from misfire procedures and safely extracting rounds to exit procedures of personnel in the event of a misfire."

Self-propelled mortars have been a mainstay of allied European and Asian armies for a generation, and YPG has tested a variety of these systems through the years, including Germany's Wiesel Lightweight Armored Mortar.

Defense

YPG's expertise with mortars extends to testing sophisticated defensive measures against commonly-available, often low tech, weapons. Though improvised explosive device (IED) attacks became an indelible image of the Iraq war in the popular consciousness, mortars were the primary weapon of choice for insurgents in the earliest days of the conflict. Today's commonly available technologies to combat mortar attack, such as Counter Rocket, Artillery, Mortar (C-RAM) systems, the Lightweight Counter-Mortar Radar, and the Q-47 Fire Finder radar, were rapidly and extensively tested at YPG.

Since insurgents tend to use commonly available Soviet-era mortars of irregular calibers, YPG testers do likewise when putting defensive systems through their paces.

Future

YPG has conducted mortar testing since its inception in 1951 and all signs point to this important mission continuing to be a vital mission element.

"Our customers like working with YPG because we can get the job done quickly and without interruption," said Jonez. "We have relatively favorable weather year-round and provide enough space to test without having to worry about affecting populated areas. We have many repeat customers and get new business all the time. YPG is without a doubt the premier test facility in the nation."

Page last updated Thu April 12th, 2012 at 00:00