By John B. SnyderJune 5, 2012
WATERVLIET ARSENAL, N.Y. -- The Watervliet Arsenal's young warriors have a lifespan of about 30 seconds, but what a wonderful life they will have. If their forefathers could speak, they would tell the world about all the places they have served, from the islands of the South Pacific to the deserts of North Africa to the mountains of Afghanistan.
But don't feel sorry for these short-lived hardened fighters because they have been well appreciated by artillerymen and women from the time of their conception until the end of their fatigued life. In fact, seasoned cannoneers who have recently retired may have spent more time with these Arsenal warriors than they have with their own families, as they fed them, cleaned them, and nursed them back to health during their careers.
This relationship began for many in the 1970s at a place called Moway House, at Ft. Sill, Okla., where artillerymen called for fire as young lieutenants and enlisted Soldiers.
Those were very tough, challenging times in the 1970s as austere budgets and troop downsizing affected the culture, as well as the morale of the force. Although jungle warfare might have been the tactics of the day given where the artillery had been for most of the 1960s and early 1970s, the focus for the artillery was redirected toward fighting a conventional army, such as a Soviet-type of force.
To match such a formable force, the U.S. Army Field Artillery had to revamp its gun systems, or what the Watervliet Arsenal affectionately calls its "warriors."
The Army closed out the 1960s with a wide variety of artillery delivery systems such as the 175mm M107 howitzer; the 155mm M126 self-propelled howitzer; the 8-inch M110 howitzer; the 105mm M137 lightweight towed howitzer; and the 105mm M103 self-propelled howitzer.
The Watervliet Arsenal, working hand-in-hand with the Army's Benét Laboratories, was instrumental in the research, design, prototype development, and the production of the tubes and various assembly parts for each of these warriors. They were truly state-of-the-art at the time and initially offered a superlative response to any Soviet artillery systems.
But in a place where achieving the standard is not good enough, Benét and Arsenal technicians knew they had to do better.
The first 1970s major weapon modernization program at the Arsenal involved the production of a 105mm main gun for the upgraded M60A1 tank. In 1973, the Arsenal manufactured 150 complete guns. But by 1977, the Arsenal was manufacturing more than 1,800 guns a year.
Although there was tremendous growth of the tank gun program in the 1970s, it paled in comparison to what the Arsenal was doing for the field artillery. The Arsenal leveraged its state-of-the-art technology to not only improve its processes, but also to increase the range and tube life for artillery systems.
Simulation Testing. What is taken for granted today was a technological marvel of the time -- simulation testing. With simulated testing, the Arsenal could take tubes and breech rings to the end of their fatigue life, without leaving the Arsenal. A fatigue life is the number of rounds that a tube or breech can be fired before it reaches catastrophic failure.
This type of fatigue simulation testing has saved millions of dollars in development test costs, as well as dramatically reducing the time required to fatigue test a tube or breech from months to weeks. Typically, live firings of a single tube at a proving ground can be accomplished in about a week, with 100 rounds being fired a day. Laboratory hydraulic-fatigue cycling at the Arsenal is capable of simulating about 1,000 rounds a day in comparison.
Swage Autofrettage. The hydraulic autofrettage procedure used in the early 1970s was an expensive, difficult, slow, and sometimes dangerous procedure where pressurized hydraulic fluid, on the order of 100,000 psi or greater, was pumped into the bore of the tube to apply compressive residual stress at the bore.
The autofrettage process imparts a deformation to the bore of a cannon tube in order to increase the ballistic pressure sustaining capability of the tube. In other words, the tube that has been autofrettaged will be capable of withstanding a higher internal ballistic pressure than its non-autofrettaged counterpart without going to a thicker tube wall.
The swage autofrettage process developed and implemented in the late 1970s by contrast, is a significantly less expensive, easier, faster, and safer process that produces much more controllable results and is much better suited to high production rates. In the swage autofrettage process, a precision high-strength mandrel is pushed through an undersized bore of the tube to permanently enlarge the bore prior to final machining. By varying the relative size of the cannon bore, the entire length of the tube can be autofrettaged to different amounts in a single pass of the mandrel. Because no special end seals, high pressure pumps and lines, or expensive external restraining fixtures are required, the swage autofrettage process has been greatly simplified, as well as made the process safer for the machinist.
Rotary Forge. Prior to the 1980s, cannon tube forgings were obtained from commercial forging houses as conventional tube forgings, that is in a near shape and length to the actual finished cannon tube. The conventional forging thus obtained was unique to a specific cannon tube design and configuration, was heat treated, and ready for machining. The initial procurement of conventional tube forgings could take up to 18 months or more and the ability of commercial forging houses to supply large quantities of tube forgings in a rapid time frame to support production requirements was problematic.
In the late 1970s, the Arsenal sought to create an in-house capability to produce tube forgings by using new rotary forging equipment. The rotary forge provides the capabilities to forge cannon tubes on essentially a moment's notice, to almost any external shape and configuration required for any cannon, and is capable of very high production rates.
The rotary forging process starts with a very generic short, thick walled, hollow-cylindrical steel shape that is typically about 10-feet in length. This raw material, or preform as it is commonly called, can be used to produce cannon tube forgings for different cannons, and is therefore not unique to a particular design.
In the rotary forging process, a preform is heated to nearly 2,000 degrees to soften the steel and then rotated over a mandrel and advanced horizontally under hammers to shape the hot forging to near finished tube geometry. This forging is then moved through associated heat treatment furnaces for quenching (rapid cooling) and toughening to desired mechanical strength property requirements. All of these processes are computer controlled.
Higher Strength Steel. In general, the higher the strength of the gun steel used in a particular cannon design, the lighter the cannon can be. Also, higher strength material allows the cannon to be fired at greater pressures for improved performance and range. As with most things in life, nothing comes for free. As the strength of gun steel is increased, resistance to fatigue failure and cracking under high pressure decreases. Put another way, as strength, pressure, and performance increase, cannon life decreases, sometimes dramatically.
In order to achieve acceptable fatigue resistance, the majority of artillery cannon designs up to the 1970s used gun steel at strength levels of about 160,000 psi yield strength. Some of the "newer" cannon designs in this era, such as the original 175mm M113 Gun on the M107 Self-Propelled System, experimented with what were considered very high strength steels for the time with gun steel strength levels about 180,000 psi yield strength.
Unfortunately, what was to later become the science of fracture mechanics and related fatigue failure was not well understood or appreciated at this time, and the original 175mm M113 Gun experienced premature catastrophic brittle fracture at a very low round count. Investigation of these in-service failures greatly advanced the understanding of fracture mechanics and the relationship between strength and fatigue resistance in gun steels, essentially making Benét Lab scientists and engineers the world recognized experts in fracture mechanics of high strength pressure vessels.
In a very short period of time, the original M113 Gun was significantly redesigned to lower the strength levels of the material, while using the new autofrettage process to make up for the loss of strength. The fatigue life of this replacement design was increased at least ten-fold from the original design, and in service failure was eliminated. Although this system is no longer in service with the U.S. military, it continues to provide safe and effective fire power to NATO allies.
There have been a significant amount of improvements through the last 30 to 40 years, far too many to list in this article. Despite all the improvements, however, the Arsenal warriors still only have a lifespan of about 30 seconds.
Why only 30 seconds?
If one adds up the total time it takes to safely fire rounds through a tube before the gun experiences a degradation to its mission, the total time is less than 30 seconds. For example, a LW155mm tube has a safe fatigue life of about 2,600 full-charged rounds. The time to fire just one round is about 0.01 seconds. Multiply that by 2,600 and you come up with less than 30 seconds.
As more seasoned artillerymen ready themselves for retirement, they will probably reflect on the memorable times they served alongside an Arsenal warrior in such places as Grenada, Panama, Iraq, and Afghanistan. They may think about how much they have changed during their career, as well as how much the artillery delivery system has changed since their first call for fire at Ft. Sill's Moway House.
And as senior artillerymen turn over their duties to the next generation of artillerymen and women, they should know that work continues at the Watervliet Arsenal to improve the life expectancy of the Arsenal warrior for the next cohort of artillerymen that will pick up the unit's colors -- maybe to 35 seconds.
Today's Arsenal is relied upon by U.S. and foreign militaries to produce the most advanced, high tech, high powered weaponry for cannon, howitzer, and mortar systems. This National Historic Registered Landmark has an annual economic benefit to the local community in excess of $100 million.
Benét Laboratories is a Department of the Army research, development and engineering facility located at the Watervliet Arsenal. It is a part of the Weapons & Software Engineering Center (WSEC), Armament Research, Development, and Engineering Center (ARDEC), which is located at Picatinny Arsenal, N.J.
Special thanks to Benét Labs' Robert Mysliwiec and Stephen Van Dyke-Restifo for their technical assistance in drafting this article.