Operation Snowball – a feat for Suffield

By Special to the News Stephen Murray on July 17, 2024.

@MedicineHatNews

The Canadian Blast Program at the Suffield Experimental Station (SES) was approved in early 1957. Henry Watson, Head of the Physics and Meteorological Section, was tasked with developing the program and hired four young scientists.

John Dewey and Trevor Groves concentrated on research in air-blast phenomena, while Gareth Jones’s major interest was seismic effects, craters and John Muirhead set up and ran the shock tube laboratory.

They began with 8-pound TNT charges, a few pressure gauges and one or two high-speed cameras. The effort to a simulate nuclear explosions began in 1958 with the detonation of a one-ton charge, then five-ton blasts the next year.

Because it was difficult to cast hemispherical charges that big, the team had to compare the air-blast of ground-burst cast TNT charges and those made up from a large number of brick charges arranged in a hemisphere. Nearly 300 such bricks were needed for each 5-ton charge.

The U.S. Ballistics Research Laboratory participated in one of these trials. A 20-ton charge (comprising 1,200 blocks) was tested in August 1960 with the research focus on blast, ground displacement and crater formation.

This shot was the first truly international trial. Canada, the U.S. and Great Britain established a tripartite blast line to assess the shock wave characteristics, the first time that blast gauges from the three counties had ever been directly compared.

The scale of the multi-ton trials continued to increase.

“Field Experiment 538,” carried out in August 1961, involved 100 tons of TNT and numerous Canadian, U.S. and British experiments were included. The air-blast characteristics were measured using electronic pressure gauges, photo-optical methods, aerial cinematography, and a new wire drag gauge to measure dynamic pressure. The crater characteristics were also investigated. Numerous structures and vehicles were exposed to the blast as well as hundreds of animals.

Preparation for Operation SNOWBALL

In the autumn of 1963, teams from the U.S. and Britain began concentrating at Suffield to begin work over the winter, heavy construction and other lengthy operations, initial preparations began in the winter of 1963-64.

Local contractors and labourers carried out much of the heavy work in the unusually mild winter of 1963 that proved ideal for speedy concrete construction.

Hundreds of miles of power and instrumentation wiring were laid throughout the test area. Some cables extended back to recording bunkers, some located many miles from Ground Zero. Each was tested for continuity, signal accuracy, and possible interference from other electrical equipment.

Many of the more than 100 high-speed cameras were mounted on towers in the open, requiring special precautions against the shock wave.

Others were operated inside bunkers positioned to cover separate events, and all cameras were operated from a central control post.

To reduce the dust likely to be lofted during the experiment, specific areas were either oiled or tarred.

Eight agencies in Canada, six from Britain, and 17 from the United States fielded more than 100 experiments.

The targets included shelters, trenches, bridges, vehicles, guns, radars, missiles, communication masts, mannequins, animals, and troops.

Fundamental Studies of Air Blast and Ground Motion

Canada’s main interest in these nuclear blast simulations was to develop an understanding of the blast dynamics, while the U.S. and U.K. were more focused on the survivability of equipment and personnel.

High-speed photography had become an increasingly important tool in shock and blast studies.

Much of the SES effort concentrated on the physics of shock and blast waves and the measurement of their rate of travel by photo-optical methods. In this experiment, the shock wave’s passage in free air would be photographed against a prepared backdrop.

The backdrop comprised a series of 50-foot by 30-foot sheets of canvas, each painted with a pattern of black and white stripes. The massive frames for the canvas sheets extended for almost a mile from the charge.

The effective height of the backdrop was extended by means of smoke rockets fired immediately before detonation. The series of high vertical white trails provided sense of perspective against which the shock wave could be tracked against the sky.

To improve the contrast with the background sky, crude oil was burned in a trench 4,000 feet behind the smoke trails.

A Royal Canadian Air Force Neptune aircraft passed directly over Ground Zero at 18,000 feet to photograph the fireball. As was the case in earlier trials, all three countries made blast measurements along a tripartite gauge line, as well as in the vicinity of their individual experiments.

Rippling ground

A method known as “coloured columns” was used to study soil deformation and displacement. The U.S. Waterways Experiment Station developed the method over many years and shared it with the young Canadian scientists.

Holes were drilled across the target area along radials from the charge, up to 80-feet deep directly under the charge.

Soil sample tests determined the structure and composition of the underlaying ground, and the holes were backfilled with a coloured mixture of sand, lime and dust, then tamped to the theoretical density of the undisturbed ground.

The result was a series of coloured columns whose deformation could be measured after the trial by digging a trench in the ground that passed through the vertical axes of the columns.

In addition to the coloured mixture, small sample tins containing this mixture (including an identification tag) were dropped into the holes at regular depths to serve as marker horizons showing vertical displacement.

The tins would also serve to identify materials ejected from the crater.

The addition of sample tins was an improvement on the method proposed and implemented by Canada. The Neptune aircraft mentioned above also participated in the target response program and provided low-level post- shot photographic coverage of the crater.

Fielding of Canadian Military and Civilian Targets

The Canadian Army deployed a company safely in trenches constructed at a distance from Ground Zero corresponding to 1 psi overpressure, an exercise designed to familiarize the 100 troops first-hand with the sensation of blast effects.

Another Canadian Army project was to check and evaluate respirators when subjected to shock waves. These were installed on mannequin heads at a variety of overpressure levels and were protected from dust and the elements by plastic covers until detonation day.

A third project of army importance was the fielding of several M113 armoured personnel carriers to see how they withstood the blast – the Canadian Forces had ordered 600 of the vehicles.

In a joint project with Britain, M-19 anti-tank mines were left exposed to assess the direct effects of shock waves on mine bodies and fuzes.

On the civil defence front, Canada’s Emergency Measures Organization (EMO) tested several new fibre-glass shelters designs. These bomb shelters were fitted with sensors and buried at various depths and distances from Ground Zero to evaluate the effect of pressure changes and ground shocks.

Assembly and Detonation of the Charge

Six days before detonation, work began on building the charge.

A shelter was first erected to protect the charge from dust, sunlight, and particularly from electrical discharges in the atmosphere. This building was fitted with wheels to facilitate its removal before detonation. The charge was assembled not unlike how a pyramid would be built, block-by- block. The cast blocks of TNT were placed in carefully calculated positions to form a 500-ton charge.

Preparation of this massive charge for complete and instantaneous detonation was another of SES’s main contributions to the program.

Casting the TNT Blocks

Casting the TNT for the charge constituted one of the trial’s major undertakings. The explosive material was cast in its entirety at Suffield beginning two years earlier.

Molten TNT was poured in molds and cooled for about 5 hours. Each of the 30,678 blocks was weighed and inspected for physical flaws before the 32.6-pound blocks, each measuring 12X12X4 inches, were moved to storage magazines.

Detonation of the Charge and Some Important Results

The test yielded valuable information about the response of military and civilian targets, as well as knowledge about air blast and cratering phenomena.

After the denotation, scientists spent months recovering and studying material on the testing ground.

Excavation of portions of crater, which began filling with water around a newly formed cone or earth at its centre shortly after the blast, took several months. Those cross sections and the pilings lead to decades of work by researchers hypothesizing on the formation of craters on the moon.

Shock and blast wave data was checked by scientists in the Canadian Blast Program against previous blasts and work began to replicate the 500-ton blast with two more later in the decade.

Thursday’s edition of the News will include a report in to some of the important finds of the blast.

(Stephen Murray is a retired defence scientist who worked at Defence Research Suffield. This is an abridged version of a forthcoming book Murray plans to release on his career and specially on the Canadian Blast program. He is based in Medicine Hat.)

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