Prologue Magazine

Summer 2003, Vol. 35, No. 2

Safeguarding Hoover Dam during World War II
By Christine Pfaff

Hoover Dam Close-up of a section of Hoover Dam, 1942, by Ansel Adams. (NWDNS-79-AA-B04)

As the Great Depression deepened in the early 1930s, a monumental civil engineering project known as the Boulder Canyon Project captured the nation's attention and stirred its imagination.

Coming amid widespread poverty and unemployment, the massive project not only provided jobs to thousands of unemployed men but offered some of the most complex engineering challenges ever tackled. Perhaps as important, it asserted America's ability to overcome extreme adversity with technical ingenuity, physical prowess, and unwavering resolve.

The project's goal: Build a huge dam— the largest ever built— across the Colorado River on the Nevada-Arizona border to harness the power and riches of the mighty river. Completed in 1936, Hoover Dam,* through the generation of electricity and the orderly dispersal of its waters, fueled the incredible growth of southern California— its large cities, its industrial base, its massive agricultural industry— and created Lake Mead, the world's largest man-made reservoir.

The construction saga and tremendous impact of Hoover Dam have been chronicled countless times over the past seventy years. Few people are aware, however, of the measures taken during World War II to maintain the dam's safety and very existence.

Tucked among the myriad official government documents housed in the National Archives and Records Administration are a series of plain brown files marked "confidential." They reveal the as-yet-untold and riveting story of the government's efforts during World War II to thwart potential sabotage of one of the nation's most strategic and vulnerable targets— Hoover Dam.

At stake was the electrical power it was providing to southern California, home of some of the nation's biggest defense plants, where planes and tanks and other armaments would be built on a round-the-clock basis once America's mighty industrial machine went to war.


The concrete in Hoover Dam had barely set when the first uneasy rumblings of a potential war in Europe were felt abroad, but it all seemed far removed from the remote Nevada desert where the world's highest dam had risen from the depths of Black Canyon to straddle the mighty Colorado River.

President Herbert C. Hoover, himself an engineer, approved funding for construction of the dam in 1930. The multipurpose structure would store irrigation water, provide flood control, and generate power to fuel the fast-paced growth of southern California. In designing and building the dam, U.S. Bureau of Reclamation engineers were tasked with some of the most difficult engineering challenges ever faced. When the last bucket of concrete was placed in the dam on May 29, 1935, the staggering 660-foot thick base almost equaled its height of 726 feet.

Security and law enforcement at the Boulder Dam Project evolved. Aside from the formidable technical and construction challenges, Reclamation was faced with handling safety, security, and law enforcement issues from the outset, since the project was located on lands ceded to the federal government by the state of Nevada. A small ranger force was created, consisting of nine Reclamation employees who were deputized as U.S. Marshals.

Early on, concerns centered on policing the Boulder City Reservation, home to the thousands of workers on the project. But after the dam opened, Reclamation's safety and security concerns shifted to the dam and powerhouse, where throngs of eager visitors were guided past gleaming turbines and generators. Reclamation, not in the business of catering to tourists, teamed up with the National Park Service, which took charge of developing the newly created Lake Mead for recreational purposes, leaving Reclamation in charge of tourist facilities at the dam and powerhouse.

Protecting Hoover Dam against human as well as natural-caused damage was soon to become a critical issue— and a contentious one at that.

As Hitler's violent aggression accelerated in Europe and the Japanese army marched against its neighbors across the Pacific, Reclamation, and even the public, became more sensitive to possible enemy threats to the dam. Many visitors expressed concern about sabotage and wondered what precautions were being taken to prevent it. By 1939, reverberations from the escalating war directly reached remote Hoover Dam.

The possible effects on the dam of an emergency situation in the United States were described in a letter dated August 30, 1939, from Reclamation's acting commissioner, Harry W. Bashore, to Solicitor of the Department of the Interior Nathan Margold.

"It might be necessary to close Boulder Power Plant to the public, and to arrange for special policing of other structures and plants to provide protection from possible saboteurs," Bashore wrote. "At the outset, however, probably an additional watchfulness on the part of our own personnel would be sufficient."

The advice was timely. In early October, a ranger observed a German man accompanied by a woman taking large numbers of photographs in the vicinity of the dam. The ranger overheard the man severely reprimanding the woman for spoiling some of the pictures and said that it would necessitate retaking them. The ranger watched for the couple's return without results.

Heightened tensions across the country prompted Secretary of the Interior Harold Ickes to contact the War Department regarding the advisability of releasing certain printed materials to the public. Secretary of War Harry H. Woodring told Ickes that detailed plans and specifications of large dam structures should be restricted and under no condition be furnished to foreign governments. He also recommended increased security precautions at the federal dams themselves.

The War Department believed that personnel working at the dams were the greatest danger and should be carefully scrutinized. Visitors were also potential threats and should not be allowed to carry suitcases, parcels, etc. into the dams.

In response to Woodring's letter, Ickes wrote that the distribution of detailed plans and specifications would be restricted as requested. Regarding the suggested investigation of all employees to ensure their reliability and loyalty, he said the department had no funds appropriated for such work. Lastly, Ickes reflected that it would be advisable to apply the army's regulations governing tours of its installations to all federal facilities.

Within a few weeks, another report of possible sabotage to Hoover Dam instantly raised security concerns to new levels. On the evening of November 30, 1939, the State Department received word from the U.S. embassy in Mexico of an alleged plot to bomb the intake towers at the dam. German agents discovered in Mexico City were planning the attack in order to paralyze the aviation manufacturing industry located in Los Angeles. This would be accomplished by cutting off power transmission over the dam's high-voltage lines. Two German agents living in Las Vegas, one of them an explosives expert, had reportedly made a dozen trips to the dam to investigate the feasibility of the plan. They intended to attach bombs to the intake towers from a boat, which they would rent under the pretense of a fishing excursion.

The State Department immediately contacted Reclamation Commissioner John Page and advised that all navigation on Lake Mead, particularly in the vicinity of the dam, be suspended without delay. Page was told to keep all information regarding the plot highly confidential so as not to reach the public or the press. Reclamation instantly banned all private boats from Black Canyon. Within a few days, the agency announced further restrictions upon employees of and visitors to the dam. Employees would not be allowed to enter the dam except when on duty without special permission and would not be allowed to take anyone else into the dam without specific authorization. To enhance security, Reclamation increased its ranger force by several men, and the National Park Service increased its patrol activities on Lake Mead.

The new restrictions led to all sorts of speculation and rumors among employees, the public, and of course, the press. On December 7, 1939, A. E. Cahlan, a columnist for the Las Vegas Evening Review, described some of the rumors circulating, including that of a large net stretched across the lake just above the dam to catch any explosives. The writer reported that Reclamation denied all suggestions of a plot to sabotage the dam and insisted that the extra precautions were merely a response to the uncertain times.

Cahlan also shared with his readers a conversation that he had had with Frank Crowe, general superintendent of Six Companies, Inc., the builders of Hoover Dam, when the dam was nearing completion. He had asked the construction supervisor about the possibility of an attack on the dam. Crowe replied: "It can't be done. It's too massive a structure, too well built. Aerial bombs might knock off a few chips of concrete but could not materially damage the structure. And besides, the air currents, and general terrain are such that planes could hardly get close enough to make a direct hit."

However, the threats were taken seriously by Reclamation. The day after he received news of the possible sabotage plot, Page consulted with the Federal Bureau of Investigation (FBI) in regard to the organization and adequacy of Reclamation's police force assigned to protecting the dam and powerhouse. On December 9, 1939, he requested that the FBI send staff to the dam to assess the security in place and make recommendations for improving it.

Other precautionary measures were instituted at the dam. Floodlights were installed to illuminate the channel above the intake towers. The rumored wire net was hung from a cable across the lake, making it impossible for boats to get within three hundred feet of the intake towers. All of this was done with the greatest care to minimize disturbance to the visitors.

Other suspicious activities at the dam in late December further pointed to possible espionage. One evening, a National Park Service patrol boat was fired on by a rifle from the steep canyon wall. The bullet ricocheted on the water and luckily missed its target. Another night, a car was spotted hastily driving away from the switchyard, which was clearly posted as a no-trespassing zone. These and several similar incidents heightened awareness and precautions even more.

In early January 1940, J. Edgar Hoover, director of the FBI, reported to Page on the results of its survey at Hoover Dam. The report addressed physical security deficiencies as well as an assessment of the employees. Among the latter, no subversive activity was noted, and their loyalty was deemed "favorable." The FBI study concluded with thirty-eight recommendations, including increased security patrols at the dam and its vicinity; securely locking off specific areas of the dam; regular inspections for foreign materials that may have been deposited in key locations; and closer scrutiny of individuals, tour groups, packages, and vehicles entering and leaving the dam. The FBI also suggested that heavy metal gates be installed to create manned inspection stations in the roadways leading to the dam from Boulder City on the Nevada side and from Kingman on the Arizona side. Lastly, the FBI proposed that it be invited to conduct a security training school for the rangers and other appropriate personnel. Some of the recommended actions had already been implemented; others were considered good ideas by Reclamation; and a few were questioned as to their practicability.

Rumors of sabotage continued to fly in the media, prompting an official press release from John Page on January 9, 1940, in which he stated, "Boulder Dam is perfectly safe. There has been no 'plot' unearthed. Reports that the Bureau of Reclamation is fearful that someone will dynamite the dam are ridiculous. All rumors and reports that visitors are no longer welcome at Boulder Dam are entirely erroneous."

Although Reclamation continued to deny to the outside world any concerns about the safety of the dam, within the government it was an entirely different matter. On January 15, 1940, a resolution was submitted to the House of Representatives (H. Res. 356) directing the secretary of state to respond to numerous specific questions regarding the "conspiracy" to bomb Hoover Dam. The resolution was referred to the House Committee on Foreign Affairs, which recommended against passage due to security concerns. Instead, the Department of State furnished the House with information that was "consistent with the public interest."

In February 1940, the possible plot to sabotage Hoover Dam resurfaced with more frightening news. The War Department forwarded strictly confidential information to Reclamation that "Life and death orders have been given by Berlin to put L.A. in the black. Two large steam electric stations, one at Long Beach and one at some point below there, are going to be blasted. Last week German sabotage experts departed from Habana, Cuba, going through Miami. They are now residing in Long Beach. Unless quick action is taken, some terminal transformer station somewhere near Boulder Dam and another station in Los Angeles are doomed also to be sabotaged."

Discussions intensified within Reclamation to increase security measures at the dam, powerhouse, and Nevada switchyards. Additional gates, barriers, and doors were ordered at various strategic locations, and a scheme was developed to install heavy wire fencing on the surrounding cliffs. In mid-June, the FBI conducted its security training at Hoover Dam for 149 men. The lead trainer, M. E. Gurnea, conjectured that attempts to damage Hoover Dam would occur by stealth and not by force, except in a getaway in the event of discovery. Protective measures should be implemented based on that premise. Gurnea cautioned that the situation would change should the United States enter into the war, at which point additional security in the form of a military guard would be advisable. Gurnea suggested increasing the numbers of rangers patrolling the dam, powerhouse, and switchyard.


Despite all the precautionary measures instituted by Reclamation, the Department of the Interior was apprehensive that the potential dangers were beyond its ability to handle. On June 19, 1940, acting Interior Secretary E. K. Burlew wrote to the secretary of war asking that the military furnish armed guards to patrol and protect the project features. The response received from newly appointed Secretary of War Henry L. Stimson was not favorable. On July 18, he wrote: "In the event of a threat of sabotage on a scale that could not be met by the local guards, the Commanding General, 9th Corps Area, has authority to act without reference to the War Department. But no such threat is known to exist now. It would be uneconomical and unsound to dissipate our military strength using troops, which should be training for combat, to perform duties which can be performed efficiently by civilian guards and watchmen."

Reclamation then inquired if the War Department would at least be willing to substantially increase the small arms and ammunition for the rangers assigned to guard against sabotage. This request was also denied on the basis that all stocks of government arms and ammunition would be needed to meet the needs of the army. However, the Interior Department obtained clearance to purchase the equipment commercially. Congress also recognized the gravity of the situation, and on May 29, 1940, Senator Patrick McCarran of Nevada introduced a bill (S. 4066) to establish a fortified military post on federal land at or near Boulder Dam to provide adequate protection for the structure against injury or destruction.

Subsequent purported sabotage incidents in early July 1940 provoked further anxiety of a possible attack on Hoover and the need for increased vigilance. A Reclamation warehouse at Parker Dam was burned down, and in the ruins, fragments of an "infernal machine" were discovered. At the World's Fair grounds in New York an "infernal machine" hidden in a suitcase exploded, killing two detectives.

That summer, two fascinating proposals for protecting the strategic dam were submitted to Reclamation. No longer focused just on small sabotage attempts, both plans addressed direct bomb attacks, reflecting heightened fears. The first came from J. P. Durbin, a concerned resident of California, who had visited the dam frequently during construction and thereafter. Durbin suggested construction of a steel and concrete canopy arched over the narrow canyon to cover the dam facility. Rock and gravel added to the canopy would provide further resistance to damage from bomb attacks.

The second proposal was voluntarily submitted to the secretary of the interior by Oskar J.W. Hansen, the Norwegian-born sculptor who had recently completed the now famous pair of huge bronze winged figures at the dam. Hansen conjectured that Hoover Dam would be an easy aerial target for a determined enemy to find and destroy. He further speculated that Hoover Dam would be a first objective and would be prone to attack prior to a declared state of hostilities.

He proposed anchoring steel cables into the canyon walls to form a protective grid over the vital parts of the project. These cables would be installed in a staggered formation so they would not all be in the same horizontal plane. The upper cables, which would suffer any initial impact, would have tough armor-plated "shields." Deflected bombs would tumble downward against each successive cable grid and detonate before ever hitting the dam.

Hansen sent his proposal to Ickes on July 14, 1940, and asked for a meeting with him to discuss the plan and present sketches and drawings. On September 12, 1940, Hansen got a letter from Page asking for the sketches and drawings as soon as possible.

By then a number of incidents had upset Hansen, and he responded in a long letter to Page that he had destroyed the sketches. Also, Hansen had traveled to Washington at his own expense in hopes of meeting with Ickes and was "put off" for three days, then told that Ickes was too busy to see him and was not interested in matters of national defense.

Acting Reclamation Commissioner Bashore then sent a telegram to Hansen, urgently requesting the sketches. This time the response from the artist was much terser. He wrote on September 22, 1940: "You folks have some nerve to wire me for my time and efforts" when he was still awaiting a final payment of five hundred dollars from Reclamation. At the end of October 1940, reference is made to awaiting Hansen's recommendations in a letter from Stimson to Ickes. No final report from Hansen was found among the Archives records, and his concept never went beyond words.

Although the War Department had been unwilling to provide armed guards or ammunition to assist in the protection of the dam, it did send an army officer there to assess the adequacy of the security in place. In September 1940, Col. E. A. Stockton, Jr., conducted the review and submitted a report. Although Reclamation had done much to strengthen protection of the dam from sabotage, Stockton recommended additional measures. Commissioner Page, upon reviewing the findings, concurred that extra vigilance at Hoover Dam was mandatory: "As I view it, we have a public trust at Boulder Dam greater than that represented by the ordinary public works. The dam is a symbol as well as a vital factor in the water and power supply of the Southwest." Page felt that due to the dam's special significance, the public had a right to visit it, and everything possible should be done to keep it open. More than half a million people visited the dam each year. Page authorized immediate implementation of most of Stockton's suggestions including augmenting the number of rangers (who by then totaled thirty-six), providing them with more effective arms, completing the protective fencing project, constructing a concrete powder house, and installing gates across the main Arizona and Nevada approaches to the dam. Page recommended further study of Stockton's proposal to install a deep submerged net to protect the intake towers from subsurface bombs or torpedoes.

In December 1940 the army announced that it planned to establish a cantonment with a force of some eight hundred men in or near Boulder City. Speculation ran high that the purpose of the post was to provide protection for Hoover Dam. Rumors also flew that the army intended to enforce martial law in the community— news that was not well received by the residents or by the Interior Department. Those fears were put to rest when Stimson informed Ickes in January 1941 that the War Department had no plans whatsoever to establish martial law. A few months later, on April 24, an article appeared in the Washington Post with the headline, "Army to Send 850 to Guard Boulder Dam." In fact, the military had no intention of assuming protection of Hoover Dam and the power plant. The new military police camp at Camp Sibert would be used primarily as a training facility. The War Department made it very clear that the military police would not substitute for Reclamation's ranger service but might be available to assist at times. In July 1941 Reclamation and the U.S. Army approved an agreement whereby the latter would patrol the switchyards adjacent to the dam, the Boulder City water system, and other outlying facilities. The army also offered to provide a convoy service to accompany vehicles across the dam. It was understood that the troops might be called away on very short notice.

Safeguarding Hoover Dam, Part 2


* Both the names Hoover and Boulder have been used for the dam. In 1930, Interior Secretary Ray Wilbur announced that the dam would be called Hoover Dam, and Congress affirmed the name to honor the then-President of the United States. After Roosevelt took office in 1933, the dam, which was actually built in nearby Black Canyon, was frequently called Boulder Dam or Boulder Canyon Dam allegedly because Roosevelt's Interior Secretary, Harold Ickes, did not like Hoover. Therefore, when quoting documents from the time, Boulder Dam is often used. In April 1947, an act of Congress signed by President Truman officially confirmed the name as Hoover Dam.


Christine Pfaff is a historian with the U.S. Bureau of Reclamation in Denver. She researches and writes about water development and irrigation projects throughout the West.

Articles published in Prologue do not necessarily represent the views of NARA or of any other agency of the United States Government.
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