Engineering with Explosions:

Project Plowshare's Pre-Gondola Experiments in Northeastern Montana

In the heady days of the Cold War, the U.S. government, through the Atomic Energy Commission (AEC), embarked on a controversial program known as Project Plowshare. The audacious goal of Plowshare was to explore and implement "peaceful nuclear explosions" (PNEs) for various civilian and industrial applications. Proponents envisioned using nuclear detonations for large-scale earthmoving projects, such as excavating canals, creating harbors, developing underground storage for natural gas, and even stimulating oil and gas production. While most of the better-known Plowshare tests, like Sedan, took place at the Nevada Test Site, a series of crucial chemical explosive experiments, known as the Pre-Gondola series, were conducted in the remote reaches of northeastern Montana, near the Fort Peck Reservoir. These tests, Pre-Gondola I, II, and III, aimed to lay the groundwork for understanding cratering mechanics in specific geological conditions, specifically weak, wet clay shale, before any potential nuclear detonations were considered (Source 1: Wikipedia - Project Plowshare).

The choice of northeastern Montana, particularly the area adjacent to the Fort Peck Reservoir in Valley County, was strategic. The region's geology, characterized by the Bearpaw shale—a highly compacted, unconsolidated clay-shale of Cretaceous age—provided the ideal medium for these experiments. This weak, wet, and often waterlogged material presented unique challenges for large-scale excavation, and understanding its behavior under explosive force was critical for Plowshare's grand engineering designs. The site was also largely unpopulated, minimizing risks to human health and property, and the land was federal property under the control of the U.S. Army Corps of Engineers, adjacent to the Charles M. Russell National Wildlife Refuge (Source 2: Project Pre-Gondola I. Technical Director's Summary Report).

Pre-Gondola I: Calibrating the Crater in Clay Shale

Project Pre-Gondola I, conducted between October 25 and November 4, 1966, was the foundational phase of the Montana experiments. Its primary objective was to establish the basic cratering characteristics of the Bearpaw clay-shale using conventional high explosives. This involved detonating four individual, 20-ton charges of nitromethane (a liquid explosive) at varying depths of burst. These single-charge experiments were designed to gather data on crater dimensions (depth, radius, volume), lip height, and the general mechanics of earth displacement in this specific geological medium.

The four events, named Bravo, Charlie, Alfa, and Delta, were meticulously planned. Researchers measured surface motion using high-speed photography of strategically placed targets. Post-shot investigations included detailed geological and engineering property analyses of the resulting craters. The data collected from Pre-Gondola I were crucial for developing an empirical understanding of how explosives interacted with the weak, saturated clay shale. This "site calibration" was an essential step before progressing to more complex row-charge experiments, which would simulate the creation of linear excavations like canals (Source 2: Project Pre-Gondola I. Technical Director's Summary Report; Source 3: DTIC - Project Pre-GONDOLA I. Crater Studies: Surface Motion). The relatively small yield of these chemical explosions meant that their immediate environmental impact was localized, primarily confined to the creation of craters and the temporary displacement of soil, without the widespread radioactive fallout associated with nuclear tests.

Pre-Gondola II: The Row-Charge Experiment

Building on the data from Pre-Gondola I, Project Pre-Gondola II represented a significant step towards simulating large-scale excavation. Detonated on June 28, 1967, this experiment utilized a "row-charge" configuration, meaning multiple charges were detonated simultaneously in a linear array. The primary purpose of Pre-Gondola II, a nominal 140-ton experiment consisting of five charges, was to gain experience with creating linear craters in the weak, wet clay-shale (Source 4: DTIC - Project Pre-Gondola II. Airborne Lidar Observations).

The concept behind row-charge cratering was to create a continuous trench or channel, rather than a series of individual, overlapping craters. This was a direct application of Plowshare's ambitions for projects like a new Panama Canal or a sea-level canal through the Middle East. Pre-Gondola II provided vital information on how to space and depth-of-burst parameters for multiple charges to achieve a smooth, efficient linear excavation. Measurements included air blast effects, cloud development (from the debris, not radiation), cratering characteristics, and seismic responses. While the primary focus was on the physical excavation, monitoring was also conducted on dust cloud dispersion, using technologies like airborne lidar to track the movement of the debris cloud (Source 4: DTIC - Project Pre-Gondola II. Airborne Lidar Observations; Source 5: OSTI.GOV - PROJECT PRE-GONDOLA II SUMMARY REPORT). The results confirmed the feasibility of creating such linear excavations in the Fort Peck geological medium and provided crucial insights for scaling up these techniques.

Pre-Gondola III: Connecting to the Reservoir

The culmination of the Pre-Gondola series was Project Pre-Gondola III, which was executed in phases. The most significant phase occurred on October 6, 1969, and focused on an even more ambitious goal: connecting an existing row crater (likely the one created by Pre-Gondola II or a similar earlier experiment) to the Fort Peck Reservoir. This experiment used a total of 70 tons of an aluminized ammonium nitrate blasting agent, detonated in a row of five charges, specifically to remove the barrier between the existing crater and the water body (Source 6: DTIC - Project Pre-Gondola III Phase III: Connection of a Row Crater to a Reservoir).

The successful connection of the trench to the reservoir demonstrated the potential for using explosive excavation to create navigable waterways or harbor basins in waterlogged environments. This was a critical test of the "nuclear excavation" concept for civil engineering applications. Pre-Gondola III also provided data on the cratering effectiveness of the ammonium nitrate blasting agent compared to TNT, estimating it to be approximately 1.6 times more effective (Source 6: DTIC - Project Pre-Gondola III Phase III: Connection of a Row Crater to a Reservoir). Other phases of Pre-Gondola III, such as Phase I (September 1968 and November 1968), also investigated techniques for producing linear craters with initially flat side slopes, a characteristic important for long-term stability in weak materials (Source 7: Wikimedia Commons - HISTORY OF THE US ARMY ENGINEER NUCLEAR CRATERING GROUP).

The Broader Context and Environmental Legacy

The Pre-Gondola experiments in northeastern Montana were vital stepping stones for Project Plowshare, demonstrating the technical feasibility of large-scale explosive excavation in challenging geological conditions. However, the broader Plowshare program faced mounting public opposition and scientific skepticism. Concerns about radioactive fallout, seismic activity, and the contamination of valuable resources (such as the radioactivity of gas stimulated by nuclear explosions, which made it unmarketable) ultimately led to its demise (Source 1: Wikipedia - Project Plowshare; Source 8: Science History Institute - We're Going to Work Miracles).

While the Pre-Gondola experiments used conventional chemical explosives, avoiding the direct radioactive contamination of nuclear blasts, they were inextricably linked to a program that aimed to use nuclear devices. The environmental impact of these specific tests was largely localized to the immediate crater sites, involving earth disturbance and the release of conventional explosive byproducts. The sites, located on federal land within or adjacent to the Fort Peck Reservoir and Charles M. Russell National Wildlife Refuge, have been managed by the U.S. Department of Energy Office of Legacy Management since the termination of the Plowshare program in 1977. While no ongoing cleanup activities are generally required for these specific chemical explosive sites, institutional controls are in place to ensure long-term protection of human health and the environment (Source 9: Department of Energy - Plowshare, Vela Uniform, and Weapons-Related Fact Sheet).

The legacy of the Pre-Gondola experiments in Montana is a complex one. They represent a fascinating chapter in the history of engineering, a testament to the ambitious, and perhaps hubristic, vision of using powerful explosions to reshape the landscape. While the grand dreams of nuclear excavation ultimately faded, the scientific data gleaned from these experiments contributed to a deeper understanding of cratering mechanics, knowledge that continues to be relevant in fields like civil engineering and geology, even if applied to more conventional methods of excavation today. For northeastern Montana, the scars of these experiments remain, silent witnesses to a time when humanity contemplated wielding the atom for peaceful, yet profoundly disruptive, purposes.

Sources:

"Project Plowshare." Wikipedia. Accessed June 26, 2025. https://en.wikipedia.org/wiki/Project_Plowshare

Lutton, R.J. Project Pre-Gondola I. Technical Director's Summary Report. U.S. Army Engineer Nuclear Cratering Group, 1970. (Accessed via DTIC: https://apps.dtic.mil/sti/tr/pdf/AD0735717.pdf)

Redpath, Bruce B. Project Pre-GONDOLA I. Crater Studies: Surface Motion. U.S. Army Engineer Nuclear Cratering Group, 1967. (Accessed via DTIC: https://apps.dtic.mil/sti/citations/ADA395916)

Lippert, J.B. Project Pre-Gondola II. Airborne Lidar Observations. U.S. Army Engineer Nuclear Cratering Group, 1970. (Accessed via DTIC: https://apps.dtic.mil/sti/tr/pdf/AD0735657.pdf)

PROJECT PRE-GONDOLA II SUMMARY REPORT. U.S. Army Engineer Nuclear Cratering Group, 1970. (Accessed via OSTI.GOV: https://www.osti.gov/biblio/4013547)

Redpath, Bruce B. Project Pre-Gondola III Phase III: Connection of a Row Crater to a Reservoir. U.S. Army Engineer Explosive Excavation Research Office, 1971. (Accessed via DTIC: https://apps.dtic.mil/sti/citations/tr/AD0737198)

"HISTORY OF THE US ARMY ENGINEER NUCLEAR CRATERING GROUP." Wikimedia Commons. Accessed June 26, 2025. https://upload.wikimedia.org/wikipedia/commons/b/b9/History_of_the_U.S.Army_Engineer_Nuclear_Cratering_Group-_USACE-p16021coll4-195.pdf

"We're Going to Work Miracles." Science History Institute. Accessed June 26, 2025. https://www.sciencehistory.org/stories/magazine/were-going-to-work-miracles/

"Plowshare, Vela Uniform, and Weapons-Related Fact Sheet." U.S. Department of Energy, Office of Legacy Management. Accessed June 26, 2025. https://www.energy.gov/lm/articles/plowsharevela-uniform-program-sites-fact-sheet