During World War II a large portion of the German military hierarchy, all the while raging war all over Europe, Russia and North Africa, still found time to seem excessively over obsessed with destroying a variety of high priority targets in the United States. Their selection of targets were for both psychological intimidating reasons as well as the actual destruction of important war related infrastructure. Sites continually brought up for attack were, among others, New York City, Washington D.C., the defense plants in and around Detroit, and Hoover Dam. Plan after plan for one or the other came on the table. Some plans were rejected as logistically infeasible or to costly relative to the results. However, some plans, seemingly falling into both categories were tested and/or actually put into motion. One of those plans, an attack against Hoover Dam was implemented in more than one way
Of those destruction of Hoover Dam during World War II plans, one was using a submersible craft as covered in an online article titled The German Submarine Attack on Hoover Dam. The premise of the article circulates around an actual attempt late in the year 1944 by the Germans, that is the Third Reich or the Nazis as the case may be, to destroy the dam by coming up the Colorado River from the Sea of Cortez in Mexico and doing so in some kind of a submersible craft armed with a vengeance weapon.
While the submarine attack on the dam remains largely questionable and unsubstantiated in the minds of many, primarily because of any number of false or discredited accounts appearing on the internet and elsewhere usually circulating around the U-boat U-133, the German or Nazi attempt to bomb the dam is different in that it is highly substantiated, backed by reams of data and records from actual certified government agencies.
Although the U-133 attack has been discredited, and resoundingly so as found in The German Submarine Attack on Hoover Dam, in an attempt to set the scene for any kind of an attack on the dam and especially so the specific submarine attack so outlined, it opens with the same paragraph as cited below, in of which for most people is found to be a much more credible scenario. Basically the paragraph states that both the U.S. State Department and the U.S. Embassy in Mexico substantiated that in 1939, well before the war with the U.S. started and a full five years before the alleged submarine attack, German agents were already on the prowl in an effort to destroy the dam and actually arrested for doing so. The connection is of course, even after a lapse of five years of war, the Germans were STILL obsessed with destroying the dam.
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.
PROLOGUE MAGAZINE Summer 2003, Vol. 35, No. 2
In April 1942, only five short months following the Japanese attack on Pearl Harbor, the movie Saboteur was released. In the movie the hero is working in a defense plant in Southern California when a saboteur sets fire to a good portion of the plant. The hero's best friend in killed, the saboteur escapes undetected and the hero is mistakenly taken for the saboteur. He gets away and chases his friend's killer across the country. In the process he follows a series of clues that leads him to ghost town in Nevada close to Hoover Dam where he comes into contact with associates of the saboteur, a group plotting to blow up the dam. The hero passes himself off as a bad guy and joins those saboteurs in hopes of finding the killer. The saboteurs cross the country with their primary focus being to sink a battleship moored in the city New York after unknowingly their earlier attempt to destroy Hoover Dam was foiled by the hero. What is interesting is that even though the movie was released in 1942, only months into the war, production actually started well before the December 7, 1941 attack on Pearl Harbor. Even then, although you wouldn't know it today, the potential destruction of Hoover Dam at the hands of fifth columnist was beginning to take hold as a serious possibility in the public consciousness. 
BOMB ATTACK ON HOOVER DAM BY AIR
The paragraph cited above from Prologue Magazine states that two German agents living in Las Vegas, one of them an explosives expert, had reportedly made a dozen trips to Hoover Dam to investigate the feasibility of blowing it up . Their plan was clean, simple, and highly low tech. There was no elaborate equipment involved, no war machines and no massive platoons of personnel. The agents were simply going to row out into the lake in a small rented fishing boat just like anybody could, and when nobody was looking attach bombs to the sides of the intake towers by hand. Before they were able to fully implement the plan they were caught and arrested and the dam was saved from destruction. After that any known attempts to destroy the dam escalated to higher authorities, becoming more sophisticated and falling under the heavy arm and might of the German military.
Within days of the Japanese attack on Pearl Harbor, and most likely well before, the Japanese began probing U.S. radar capability up and down the Pacific coast, sometimes in doing so using already in place on-the-ground clandestine operatives. In the process, according to examples cited in The Radar Dilemma and other similar sources, they had developed a pretty good handle on where U.S. coastal radar coverage was effective and where it was weak or nonexistent.
On December 31, 1941, the IV Interceptor Command reported that several enemy planes were believed to have landed and been hidden near the inland desert communities of Indio and Brawley in the Imperial Valley of California. They also reported that five messages in Japanese code were being sent daily between Brawley and Mexico City via short wave radio. At 12:32 PM in the afternoon of December 31, 1941, the Federal Bureau of Investigation relayed the following message:
"There is a plan for air and sea attack against San Diego, San Pedro and San Francisco, to take place about dawn either New Year’s Day or the following Sunday. It is possible the attack will be made against San Diego and San Pedro first. Expecting cooperation from aliens ashore. The air attack will be by German airmen from across the border where planes are now under cover, taking off before dawn and coming over flying high. If air forces are alert, this can be broken up before they reach their objectives. Am sending you this information for want of better channels to advise. Remember Pearl Harbor."(see)
That potential attack was stopped in its tracks by one of our own clandestine operatives, an American female operative, a spy if you wish, a movie star named Rochelle Hudson who, along with her Naval officer husband, had been traveling incognito as a vacationing couple throughout Mexico before and during the early stages of the war to detect if there was any German or Japanese activity going on south of the border, and if so, how much. On one of their vacations she and her husband uncovered a supply of high octane aviation fuel stashed by German agents in Baja California. After the discovery the stash was dealt with appropriately and without the necessary fuel to implement the planned attack, it was scrapped.
After that the window pretty much closed for the enemy for any sort of a repeat because of the operational radar coverage that had been put into place up and down the coast from Los Angeles south into Mexico and both sides of the Baja. Almost any successful access to Hoover Dam by air across the 300 mile breadth of California from the Pacific or up it's underbelly via Baja was practically impossible.
That coverage of the dam, or non-coverage as the case may be, left two open access routes to destroy it. One, by water up the Colorado River, and two, by air coming through the backside over Arizona and New Mexico, both thought by the powers to be impossible to implement. The by-water route via the Colorado River using a submersible is covered quite thoroughly in:
GERMAN SUBMARINE ATTACK ON HOOVER DAM
WORLD WAR II ERA ARMY MACHINE-GUN NEST STILL ABOVE THE DAM
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The by-air route through the backdoor is generally less covered. The Germans, knowing full well from the experience of the Japanese that crossing California from the air to the dam was practically impossible. Sticking with their allies they went about coordinating an attack through a combined effort between themselves and the Japanese. Well before 1945 the Japanese had honed a serious set of plans to destroy a good part of the Panama Canal, specifically the Gatun Dam, with the attack emanating from the Atlantic side rather than the Pacific side. To do so they designed and built a series of giant, super long distance submarines, the I-400 Class, each capable of carrying three powerful aircraft.
A four-boat flotilla was assembled consisting of two of the newly designed I-400 Class submarines, the I-400 and I-401. They were joined by two smaller subs capable of carrying two aircraft each, the I-13 and I-14. In that the two smaller subs did not have the fuel capacity for the round trip to Panama, they were to either refuel from the two larger subs or abandoned after the attack. The Germans planned to use one of the subs and enter the Caribbean launching two or three planes on a one way trip toward Hoover dam from off the coast near Brownsville, Texas, coordinating the timing of the destruction of the dam with the Japanese attack against the canal --- basically coming through the backdoor and bypassing any of the west coast radar. The subs were provisioned for a four-month cruise on a route designed to take them beyond India, around South Africa and the Cape of Good Hope and out into the open Atlantic ending in the Caribbean off Panama.
I-400 CLASS SUBS CARRIED THREE AICHI M6A1 ATTACK FLOATPLANES
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However, on May 8, 1945, before the Germans were able to implement their part the the plan they unconditionally surrendered to the Allies and the plan aborted. After that, with the Japanese still remaining in the war, for whatever reason, even before they departed their home base the flotilla was reassigned to attack Ulithi Atoll in the South Pacific, where American aircraft carriers were known to be moored.
When the submarines left their base July 23, 1945, under new orders, each one departed separately, with a rendezvous set at sea for August 16th off Ponape Island, the Carolines. On August 5th while at sea the I-400 suffered an electrical fire that forced her to surface to repair the damage. The I-401 sets a new rendezvous point but the I-400 did not receive the message and the subs missed each other. The strike date was set for August 17th, but Japan surrendered on the 15th.
A lot of historians and others laugh off a potential strike against the canal. However, to show how serious the Japanese were about the whole thing, in March 1945 the submarine flotilla's air squadron moved to Nanao Bay, located on the west coast of Honshu, 178 miles northeast of Tokyo, to practice for the strike. A full-scale exact-replica model, almost down to the last nut and bolt of the Gatun Locks, even recreating the air approach, was constructed in adjacent Toyama Bay and the pilots practiced bombing and torpedoing it over and over. The squadron staff and pilots felt confident of striking their target and wrecking the huge gates at the locks, draining the lake and rendering the canal unusable.
Source: Janusz Piekalkiewicz, The Air War: 1939-1945, (Poole, Dorset: Blandford Press, 1985), 420-421
While the Germans had gone nuts over devising plans to destroy Hoover Dam in some fashion or the other --- either on their own or working with the Japanese --- the Japanese had been quietly going along developing a plan to strike the U.S. mainland in a huge, huge way, delivering a massive destructive blow without committing vast amounts of manpower, equipment, or money. The plan started small, with a two-man midget submarine being a key factor, with the final phase ending with the city of Los Angeles intending to being nuked. Re the following:
"Somewhere along the way the Japanese and their German cohorts, both working in some fashion in the development of an atomic bomb became privy to the fact that one of California's channel islands, more specifically San Nicolas Island, was quite possibly going to be used to test a nuclear device, i.e., set off an atomic bomb. Since San Nicolas was an island and islands and the sea were a purview of the Japanese, they took it upon themselves to investigate, and did so by sending a midget submarine into the area."
AND NOW THIS:
For those who may be so interested, a free, full online version of the aforementioned movie Saboteur is available below. Short extracted scenes from the movie showing the dam and the discussion of it can be seen by clicking HERE, the interesting part being the ten car limit put into place crossing the dam causing a minor traffic jam that shows up in the movie.
GERMAN SUBMARINE ATTACK ON HOOVER DAM
F6F NAVY HELLCAT, NAZI SUBS, AND
THE BAJA MEXICO CRASH SITE
1944 GERMAN ATOMIC BOMB
THE FLYING TIGERS
THE BOY IN THE MAN REMEMBERS THE LEGEND
PEARL HARBOR SURVIVOR
TWO-MAN JAPANESE- MIDGET SUBMARINE MOUNTED
ADJACENT TO THE MOTHER SHIP'S CONNING TOWER
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ON THE RAZOR'S
As to the subject of donations, for those who may be so interested as it applies to the gratefulness of my works, I invariably suggest any funds be directed toward THE WOUNDED WARRIOR PROJECT and/or THE AMERICAN RED CROSS.
WHILE AMERICA SLEPT:
The saboteurs hole up in a shack in a ghost town some distance from Hoover Dam albeit still overlooking it. The first photo shows one of the saboteurs looking through the observation hole cut in the wall of the shack while passing by on the outside. The second photo shows the view of the dam from the same hole using a telescope and the third view the hero using the telescope in the process of discovering the plot.
AND NOW THIS:
TOP NOTCH COMICS #6, June 1940:
What follows are two pages from an 11 page comic book story titled "The Attack On Boulder Dam." Believe it or not, the story actually appeared in Top Notch Comics with a cover date of June 1940, a full year and a half before the U.S. entered World War II. In the story the hero, The Wizard, attempts to thwart the destruction of Hoover Dam, called in the story under it's old name Boulder Dam. The protagonists, a formal uniformed military contingent, although identified as fictional Mosconians, are clearly Nazis. They speak with a German accent, they wear drop-ear helmets, and the insignias on their red bomber-like planes are swastikas. So here is a fully public consumption general circulation comic book published in 1940 and not necessarily aimed toward or intended for a totally sophisticated audience, clearly presenting a story about destroying Hoover Dam. Also clearly done is the comic book artist's exceptionally accurate cartoon rendition of Hoover Dam, including the intake towers targeted by the Nazi saboteurs in 1939.
FOR THE COMPLETE STORY IN ITS ORIGINAL FORM CLICK HERE
FOUR FAVORITES #3, January 1942:
Below are two pages from a 16 page comic book story that appeared in Four Favorites comics with a cover date of January 1942, barely a month after the U.S. entered World War II and probably printed or in production weeks, possibly months before the war. In the story the hero Lash Lightning attempts to halt the destructive activities of Professor Grosskop, identified in the story as a Nazi, who is trying to destroy Boulder Dam on the Colorado River as well as disrupting electricity to hinder the war effort at production plants.
FOR THE COMPLETE STORY IN ITS ORIGINAL FORM CLICK HERE
If I read either of the two comic books during their original release is not known. The 1940 one most likely not, the 1942 one possibly. Even though I was quite young at the time my ability to read started early on. The following, speaking of my older brother in the third grade, is found at the source so cited:
"By the time he reached third grade and I started kindergarten, I was reading third grade books probably as well or better than he was. Two books I remember fondly right up to this day is one about Hoover Dam showing how it was constructed, it's inner workings with row after row of power generators and one with pages of black and white line drawings of Da Vinci's flying machines."(source)
ACTION COMICS #34, March 1941:
As to the two above comic book stories making reference to the destruction of Hoover Dam even prior to the U.S. entrance into World War II, any number of people have come forward with so what, who the hell is The Wizard and that other half-baked doofus called Lash Lightning? To set the record straight, as far as the destruction dams go, even our old buddy Superman got into the act as found on the cover of Action Comics, Volume 1, Issue Number 34, with a cover date March 1941 and an in store date of January 23, 1941:
The publicity poster released by the studio for the 1942 movie Saboteur appears at the end of this paragraph. Note the four images related to the events shown in the movie are done in a very comic book manner. The upper left image clearly depicts a trench coat covered figure observing the Hoover Dam, followed left to right by the sinking of the battleship and the destruction of the aircraft factory. Again, all released just five months after the Japanese attack on Pearl Harbor and the U.S. entrance into the war.
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Below are four separate panels from the daily Terry and the Pirates newspaper strip that linked together form a tightly interrelated four day series circulating around a major character in the strip, a female pirate called the Dragon Lady. The four panel series, dating from Wednesday March 30, 1938 through to Saturday April 2, 1938 was published long before any entrance into the war by the United States. They clearly show the Dragon Lady, through the story line by the strip's artist/cartoonist Milton Caniff, setting into motion the early stages of a formal resistance group to fight the Japanese, in turn by doing so, through what was considered a rather unsophisticated medium, reaching and raising the public consciousness of the potential Asian threat.
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TWO AIRBORNE AICHI M6A SEIRANS AFTER LAUNCH FROM I-400 CLASS SUB
The previously planned submarine attack on Hoover Dam of some five months earlier had been rendered moot because of a number of mitigating circumstances, including several missteps by participants not following through at the level they should have, impacting adversely its successful completion --- i.e., the sub got hung up some 280 miles from the mouth of the river on a sandbar and some rocks somewhere east and south of Nelson, Nevada, between El Dorado Canyon and an area now flooded by Lake Mojave. In doing so that left the air attack being the only viable alternative and of the highest priority.
However, as fate would have it, the bombing run on Hoover Dam was stopped in it's tracks from moving forward to completion because of the German unconditional surrender on May 8, 1945. Initially though, as far as the bombing attack was concerned, the possibility of a surrender was not part of the equation and only came into play well AFTER a whole lot of logistics and details had been worked out. To wit:
A one way flight launched from the Gulf of Mexico just off the coast of southern Texas, say between Brownsville and Corpus Christi, to Hoover Dam is something like 1500 miles. The range of the Aichi M6A Seiran was said to be around 700 miles with a top speed of 295 MPH. If the aircraft, no matter how they were outfitted, in their standard form or otherwise, even with added fuel tanks, for the distance would require refueling, with only just one stop pushing it. Most likely a second stop would be necessary. In that the attack, as I understand it, was designed as a one way trip, a stripped down version of the plane carrying only explosives might possibly make it with one refueling stop, but not none. After the attack the planes would just be abandoned in the desert someplace and the pilots, presumably German (read white Caucasians), with the right provisions and identification could easily assimilate into the low population desert southwest, especially with assist by already in place on the ground agents.
As for refueling locations, in that the aircraft were floatplanes and most of the length of the trip was whole of the way over dry desert territory, the timing and the spots for said refueling would have to be carefully selected and worked out. So said, that leaves only a very few viable options. On the route to the dam the first of the most viable locations is Balmorhea Lake, Texas, somewhat over half way between San Antonio and El Paso roughly 600 miles from Brownsville. Continuing west the second most viable refueling spot is 600 miles away at Theodore Roosevelt Lake slightly northeast of the Superstition Mountains in Arizona. Theodore Roosevelt Lake is roughly 300 miles southeast from Hoover Dam.
The trip to the dam was said to be a one way flight. If such was he case, any need by the mother ship for water-borne recovery would be negated. So said, ejecting the landing pontoons upon take off would not only increase aerodynamics but also increase the fuel mileage in the process. It would also open any number of abandoned or isolated ground-based landing strips for refueling, eliminating the need for a water only refueling site.
It should be noted as well that I-400 submarines and Aichi M6A Seirans were both designated for use by the Imperial Japanese Navy in an attack against the U.S. west coast under Operation Cherry Blossom At Night as found in Footnote  below.
In October 1942 a Japanese midget submarine was bombed some 500 yards offshore of Redondo Beach, California. A few days after it was bombed the sub washed up on the beach just south of the Redondo pier. The fact that it was bombed and washed up on the beach, if not kept secret on the American side, was at least kept under wraps, and as far as the Japanese were concerned, the mission it had been assigned to do had already been completed.
Any follow-up of Japanese plans were in the hands of a series of faceless unnamed decision making committees in the United States, having to do with one of the channel islands off the coast of California. More specifically, was the U.S. going to use or not use San Nicolas Island as a nuclear test site? The midget submarine had been used by the Japanese to determine just such an effort. The following year, 1943, supplementing their clandestine spying endeavors on San Nicolas Island and for similar or like reasons, the Japanese dispatched at least two known operatives into the desert southwest to do radioactive soil sampling.(see)
By then, the Japanese, pretty much figured any major move involving nuclear strikes in any fashion by them would most likely not be forthcoming any time soon. Feeling the squeeze and needing a major game changer, as well as being unsure if the U.S. was capable, able, or willing to attack Japan with a nuclear weapon --- but knowing if not, or in a possible combination of the two, an invasion of their homeland was inevitable, the Japanese began putting into place another long distance inexpensive yet feasible non-manpower heavy preemptive first strike against America.
That operation, given the codename "Cherry Blossoms at Night," was finalized on March 26, 1945. The idea was to use I-400 aircraft equipped long-range submarines, each carrying three 300 mph Aichi M6A Seiran single wing attack-bomber floatplanes, loaded to the gills with bombs filled with plague-infected fleas. Although the plan was not implemented for a number of reasons, lack of sufficient numbers of I-400's and aircraft, for example, but not lack of will, the submarines were to surface off the coast of San Diego, fan out the planes over a wide area and deep as possible inland keeping high populations in mind, all the while along their routes dropping balloon bombs filled with plaque infested fleas. The end results were to infect and kill as many people as possible, with figures ranging into the tens of thousands. The Japanese, knowing the U.S. might be able to contain the spread of disease somewhat quickly within reason, chose San Diego because of its proximity to Mexico and especially so Tijuana with its high population, and most likely lack of ability of the Mexican government to respond fully to the crisis, thus not containing the spread of the disease before completion of its intended impact.
JAPANESE MIDGET SUBMARINES
OPERATION CHERRY BLOSSOMS AT NIGHT