Large caliber artillery is not unique to the modern era, nor is it unique to the Cold War where many large artillery pieces were engineered and produced. The largest artillery pieces can trace themselves back well before World War I. However, it was during World War I and the deployment of weapon systems such as the Paris Gun, that large artillery saw it's widest deployment. By World War II, the Germans had further perfected their design deploying limited installments of their V-3 gun system. However, while this enabled long range bombardment from gun systems, the introduction of the atomic bomb brought forth another series of questions for engineers: how else can we deploy this technology?
By 1948, American engineers and designers were beginning the early stages of designing and developing what would be known as the M65 Atomic Cannon, known affectionately as Atomic Annie. This 280 mm gun, originally drafted on a 240 mm carriage, was designed to deliver an atomic warhead up to twenty miles away, with a yield ranging from fifteen to twenty kilotons. By 1950, this weapon system entered the building phase. But was the 280 mm gun the only atomic artillery weapon system? Not hardly. In fact, it wasn't even the only caliber of gun in the Atomic Annie program.
"Atomic Annie" as We Know Her
The M65 280 mm Heavy Motorized Gun is the standard U.S. military nomenclature that describes Atomic Annie. This entire system has several components that make up the whole. The M249 4x4 truck situated at the front is the pilot prime mover for the gun carriage T72. The rear of this massive carriage is guided by the M250 4x4 truck that is situated at the rear. Both trucks in tandem move the gun and the carriage. The gun tube, firing control system, loader, and recoil mechanism together make up the T131 gun system - Annie's teeth.
It's important to note that Annie is based on her German counterpart: Anzio Annie, also known as the Krupp K5, that predates her by about ten years. Anzio Annie, however, was designed as a conventional railway artillery system.
Atomic Annie's payload capabilities did indeed include conventional weaponry, boasting the largest conventional artillery shell in the world that was deployed during her time (larger caliber systems had been previously deployed and used - some as large as 910 mm). However, what made her special was the atomic part. Her artillery payload was a W9 nuclear warhead that had an adjustable yield from fifteen to twenty kilotons. She was able to lob this projectile up to twenty miles away if firing into the wind.
Throughout her service life (1953 - 1963) she was deployed in Germany and Korea, used as a deterrent against potential invasion from the Red Army. While her mission would have been to either prevent or stall the Soviets, only one of these guns ever fired an atomic shell. This took place at 0830 on 25 May 1953 at the Nevada Proving Grounds. The shot, known as Grable, was one of a series of tests in the Upshot-Knothole atomic tests. All previous and following shots were using conventional 280 mm artillery rounds.
It's not my intention to bean you to death with information that is already known and reinvent the wheel. An extensive amount of research and background on Atomic Annie can be found across a few resources on the web. See links below:
Lesser Known Annie's
There are at least two lesser known incarnations of Annie. One is the purported prototype that was used to serve as the breadbox for the widely known 280 mm carriage. The suspect for this was a 240 mm gun, a conventional system, that was given the nomenclature of T1 240 mm heavy gun. The link to Annie from the 240 mm, however, is only found in the T72 carriage, and no other documented relationships can be established. For this reason, the 240 mm gun is often not referred to as a close relative of Annie.
A much more likely half sister to Annie, however, is the 175 mm Gun T145. The T145 was a smaller weapon system that was married to the T76 carriage. The gun began production at least by the mid-1950s, once again after exhaustive studies by the Franklin Institute. The T145 was also much lighter weight than Annie, coming in at just under 15,000 pounds. The T145's written history accounts are limited, but the research documents that refer to it are quite extensive. We'll go over that in another post. It's worth noting that one of the T145 guns was later modified for use in high-altitude research - the very same research that Dr. Richard Bull and HARP would be involved in during the 1960s and beyond. Nevertheless, the T145 served as the immediate replacement for Annie in locations that demanded more portability, and subsequently replaced her upon the development of smaller atomic shells.
S. Berliner, III put together a fairly substantial writeup on the 175 mm "Baby" Atomic Cannon. I'm inclined to believe the authenticity of Mr. Berliner's commentary, having been part of a team that fired these weapon systems.
As for both the 175 mm and 240 mm gun systems, a fully assembled T1 remains. However, the T145, so far that we know of, exists only in pieces. Berliner points out that the only tube for the 175 mm gun remains at Fort Sill, and judging by the pictures he made available, it is totally cannibalized.
But...what about the two that no one has reported on?
The 350 mm Mobile Gun
In a technical report (TR) from the Franklin Institute dated sometime after 31 March 1951 (no data control sheet was found), a 350 mm version of Atomic Annie is described. Rather, the entire TR outlines the engineering study of what would be the 350 mm Heavy Motorized Gun system. The projectile fired from this gun was designed to be approximately 1,500 pounds juxtaposed to Annie's 600 pound shell. For comparison, the Krupp K5 had a shell weight of just over 500 lbs. It was also designed to meet a muzzle velocity of about 3,000 feet per second, again juxtaposed to the K5's ~2,400 feet per second. Not only was the gun larger, it was capable of a much heavier shell, a higher rate of fire, and was capable of returning-to-battery faster than the 280 mm gun.
The gun was designed to be approximately sixty-five feet long and able to elevate to fifty-five degrees. The barrel was treated to approximately 120,000 psi based on data gathered from an interior ballistics study. Like the 280 mm gun, the 350 mm gun (based upon it's age, and because it's referred to in the document) drew upon ballistics data and design data from the 240 mm T1 gun. The barrel alone weighed over 85,000 pounds.
The research and design of this system had multiple applications apparently investigated. The report indicates that mortars, single recoil, and double recoil artillery were all looked at. The double recoil design is what was selected, giving a top carriage weight of around 36,000 pounds (based upon their 50,000 psi requirement), and the bottom carriage a weight of almost 31,000 pounds. This is all to say that while the 280 mm gun weighed a whopping 166,000 pounds with her carriage, recoil mechanism, muzzle, and all of her parts, the 350 mm revision would have weighed over 153,000 just with the gun tube and both carriages. The report describes that the emplaced weapon would weigh in excess of 200,000 pounds.
The weapon would be transported in three pieces: the gun tube and breech (100,000 pounds), the top carriage and cradle (90,500 pounds), and the bottom carriage (30,600 pounds), for a grand total of approximately 221,100 pounds across three loads. The T10 prime movers are described for the moving of the carriage pieces, the same as the T1 and "newer" T2 carriage. However, a new semi design was required for the larger gun tube - though the M26A1 is mentioned. No fewer than five different methods of movement are described, and none of them are conclusive.
Research conclusions reported indicate that the weapon could be designed to meet the need of a 1,500 pound projectile that has a muzzle velocity of 3,000 feet per second and a caliber of 350 mm. The report also indicates that setup time would be approximately four hours, with a rate of fire around one every three to four minutes. The range is specified to be between twenty-two and thirty-one miles.
The 420 mm Railway Gun
The document, in the section where transportation is mentioned, also suggests the potential for a "larger" caliber gun that is capable of firing a 2,000 pound shell. However, this is the only mention of a larger 420 mm caliber weapon. Further references in the TR suggest modifications on the 350 mm design to reduce the muzzle velocity and thus shortening the barrel for more close proximity shelling.
What Went Wrong
There is no indication in the document as to any obstacles in the path of the designers and engineers for the development of the 350 mm gun. At the time of publication, the Korean War was raging on and the threat from the Soviets was elevated due to their acquisition of the atomic bomb. However, it doesn't take much to understand what may have ultimately prevented the weapon system from being developed. If we consider that Annie had to be transported with two prime movers in her 280 mm incarnation and that "Super" Annie would need three separate transports for mobility, things become clear. This is especially true when considering that the region at greatest risk of a Soviet invasion was the mountainous region of the Fulda Gap, making transport even more difficult.
By the time this problem may have been solved, the project was likely overshadowed by much more mobile and lighter methods of atomic deployment. This includes the introduction of the MGR-1 Honest John and MGR-3 Little John rocket systems that were able to be deployed for the same range or further. Military doctrine by 1965 had still not removed front-line atomic weapon deployment as an option, and therefore the need continued for the use of atomic projectiles. This could be covered by the reduction of warhead size and the attaching of these shells to smaller and lighter artillery systems such as the M115 203 mm heavy howitzer. While it was developed in 1939, the atomic shell that was fitted to projectiles fired from the M115 were in development as early as 1953.
Subsequent developments on 155 mm howitzers would lead to better mobility and easier deployments of atomic shells as well, making Annie an unruly and unnecessary beast for the purpose of atomic or even conventional weapons deployment by the time she was retired in 1963.
What Went Right
As late as the 1980's, howitzers were designed and capable of firing atomic rounds. This included the still-used M198 155 mm medium howitzer. That is to say, atomic shells were totally removed from deployment in 1992 since the need for such artillery was no longer defined. In addition, revision of U.S. military doctrine had since removed the need for front-line atomic deterrents, making atomic shells entirely obsolete. The shells themselves were demilled, as the gun systems were not themselves "atomic" or "conventional."
It is important to note, that while we often discuss things as "atomic" capable, or "nuclear" capable, these words are effectively just missions. There is no real such thing as an "atomic cannon" - despite the fact that we love to use that word to describe Annie. She was indeed designed with the primary mission of delivering an atomic shell, but she was capable of so much more than that, as were her predecessors and ancestors. Many of those predecessors went on to aid in research and development of new technology ranging from weapons systems, to space flight, to the study of atmospheric weather conditions.
To say that Annie is the genesis for it all is incorrect, however. Even her namesake Anzio Annie would not fit that description. We will discuss in another research project exactly where the origins of such powerful artillery came from, and where it almost went.
In the meantime, of the twenty confirmed built 280 mm Annie's, only eight remain. Of those eight, only one is an entire M65 assembly, with the remainder all simply being the T131 gun and carriage assembly. They are indeed relics of a time long ago.
Engineer drawing of the 350 mm Heavy Motorized Gun system with carriage. This is the drawing taken exclusively from the document referenced in this article and is one of over twenty different engineer drawings.
The document was originally marked as "Confidential" when it was published in 1951. It has since been marked "Unclassified", likely sometime in the 1960s or 1970s as part of the Department of Defense's Directive 5200.10, which declassifies certain documents after twelve years. This directive is referenced within the document and indicates this document followed that schedule for declassification.