This Idaho Lake Is Hiding Something — Scientists Fear What the U.S. Navy Is Testing Beneath It

The mysteries of Lake Pend Oreille and the sea monster. Yes, we supposedly have a sea monster called the paddler. It's been seen and sighted for over 100 years. Naysayers say it's the Navy down in Bayview with their submarines because they do have a Navy base down there. More than 300 miles from the Pacific Ocean, the U.S. Navy operates one of its most unusual underwater research facilities. Not on the coast. In Idaho, at Lake Pend Oreille, Navy engineers test large-scale submarine models in water reaching roughly 1,150 feet deep. The lake covers about 148 square miles, while the Navy's acoustic research detachment occupies approximately 25 acres near Bayview. And what happens underwater is even stranger. The Navy operates four major acoustic test ranges, including a system containing 158 hydrophones and 36 underwater projectors. A one-third scale Virginia-class submarine model carries 1,680 lead-acid batteries and can operate autonomously beneath the lake. Another model represents the Columbia-class ballistic missile submarine. The Navy calls Lake Pend Oreille one of the best places in the world for this work. But why would submarine technology be tested in a mountain lake nearly 2,000 feet above sea level? The answer begins with something the Navy didn't create, the lake itself. Topic one, the 1,150-foot deep lake. Lake Pend Oreille is Idaho's largest and deepest lake. Official Navy figures place its maximum depth at approximately 1,150 feet, although older detailed surveys reported depths approaching 1,200 feet. Its surface covers approximately 148 square miles. That's what first makes it unusual. A lake surrounded by mountains contains a water column deep enough to test sophisticated undersea technology, but depth isn't enough. According to the Navy, the southern end of Lake Pend Oreille has another important characteristic. It's extremely quiet. Most rivers and major inflows enter toward the northern side, leaving parts of the southern lake unusually stable. Below approximately 100 feet, Navy researchers describe the water as having near-isothermal conditions, and much of the bottom is relatively flat. For acoustic engineers, those characteristics transform a natural lake into something resembling a gigantic outdoor laboratory. But the Navy didn't choose this place first. Ice did. Topic two, the glacier that built the laboratory. The strange depth of Lake Pend Oreille is connected to the Ice Age. Northern Idaho was repeatedly reshaped by enormous glaciers. Idaho water planning documents describe ice sheets in the panhandle reaching as much as one mile thick, gouging deep basins that eventually became lakes including Pend Oreille, Coeur d'Alene, and Priest Lake. During the last major glacial period, roughly 10,000 to 22,000 years ago, the Purcell Trench Lobe advanced across the area occupied by modern Lake Pend Oreille. The ice also blocked the Clark Fork River near Sandpoint. That helped create the enormous ice dam associated with Glacial Lake Missoula and the catastrophic Ice Age floods that repeatedly transformed parts of the Pacific Northwest. When the glaciers disappeared, they left behind an unusually deep mountain basin. Thousands of years later, those same physical characteristics would attract the U.S. Navy. But first, the Navy came to Idaho for a completely different reason. Topic three, 293,000 sailors trained here. In 1942, during World War II, the Navy established the enormous Farragut Naval Training Station near the southern end of Lake Pend Oreille. The government acquired approximately 4,160 acres for the facility. Then, the population exploded. More than 293,000 sailors eventually received basic training at Farragut during World War II. Historical records describe the wartime complex as a temporary city capable of accommodating more than 50,000 inductees. Barracks appeared. Training facilities were constructed. Thousands of recruits arrived. For a brief period, this quiet part of northern Idaho became one of the Navy's major inland training centers. Then, the war ended. The giant training operation disappeared. But the Navy eventually discovered that Lake Pend Oreille itself offered something far more valuable, a controlled environment for understanding how submarines sound underwater. Topic four, why the Navy stayed in Idaho. By the 1960s, the Navy had transferred part of the former wartime operation into what eventually became Carderock's Acoustic Research Detachment. The reason was the lake. Deep water, low background noise, a relatively flat bottom, stable temperature conditions at depth, and none of the enormous logistical problems associated with open ocean testing. Testing a submarine in the ocean is expensive. Ships are required. Weather changes. Waves generate noise. Commercial traffic interferes. Ocean currents complicate measurements. At Lake Pend Oreille, engineers can operate in a much more controlled environment. The Navy describes it as Idaho's quietest body of water and an ideal location for acoustic research. The result is extraordinary. A mountain lake hundreds of miles from the coast became a testing ground for technology intended for some of the most advanced submarines on Earth. And this is exactly the kind of hidden American landscape we investigate on Discover Tube. Because what looks like an ordinary Idaho lake from the surface contains an underwater research system almost nobody realizes is there. Topic five, the world's largest unmanned submarine. One of the most unusual vehicles at Lake Pend Oreille is called Cutthroat. Officially, it's Large Scale Vehicle 2, LSV-2. The Navy described Cutthroat in 2022 as the world's largest unmanned submarine. It isn't a toy-sized research model. Cutthroat is a one-third scale representation of a Virginia-class submarine. Its predecessor, LSV-1, represented a Seawolf-class submarine at one-quarter scale. Why build something this large? Because small models cannot reproduce every acoustic and structural behavior of a full-sized submarine accurately. Larger models allow engineers to capture more of the important physical characteristics while avoiding the enormous expense of repeatedly modifying an operational submarine. And Cutthroat contains systems that begin to reveal just how serious the model is. Topic six, the 1,680 batteries. The front section of Cutthroat is dominated by batteries. According to the Navy, the main propulsion motor alone is supplied by 1,680 lead-acid batteries. The vehicle also carries onboard computers and autonomous software, allowing it to operate on the test range. During a typical test, Cutthroat moves between underwater sensor arrays. Engineers record the sound it generates. They measure how different components affect its acoustic signature. Then, the data is used to predict how a full-scale submarine would behave. Preparing, operating and analyzing one typical LSV-2 underway is so demanding that the Navy says roughly one-third of the acoustic research detachment workforce can be involved. The objective isn't speed, it's silence. Because underwater, sound can reveal where a submarine is. Topic seven, why submarine noise matters. A submarine's greatest advantage is its ability to remain difficult to detect. But almost everything aboard can create sound. Propulsion systems, machinery, water moving around the hull, vibration, pumps, propellers or other propulsors. Even subtle structural behavior can produce acoustic signatures that travel through water. At Lake Pend Oreille, engineers can isolate and measure those signatures under controlled conditions. According to NAVSEA, work conducted at Bayview has contributed to improvements involving propulsors, bow designs, acoustic treatments, sonar systems and other submarine features. The official mission includes research into structural acoustics, hydroacoustics, propulsor development and reducing target strength. And to measure all of this, the Navy installed an enormous listening system underneath the lake. Topic eight, 158 hydrophones underwater. One of Lake Pend Oreille's most remarkable installations is the Intermediate Scale Measurement System, or ISMS. The Navy describes it as an extraordinarily complex underwater structure. It contains 158 hydrophones and 36 projectors. Hydrophones are essentially underwater microphones. They detect pressure waves traveling through the water. The projectors can generate controlled acoustic signals. Together, the system allows engineers to measure radiated noise and investigate how underwater objects interact with sound. This includes target strength testing, measuring how detectable an object may be when exposed to sonar. Instead of sending a new submarine directly into open ocean trials for every design experiment, engineers can test scaled configurations in Idaho first. And ISMS is only one of four major ranges operating on the lake. Topic nine, four secretive test ranges. The Navy publicly describes four major acoustic ranges at Lake Pend Oreille. The first is a buoyant vehicle range. A system can pull a model down toward the lake bottom while onboard instruments collect data. The second is the LSV range used by vehicles such as Cutthroat. It includes two vertical acoustic arrays with the submarine model traveling between them while sensors measure radiated noise. The third is ISMS with its 158 hydrophones and 36 projectors. And then there's a fourth installation associated with a distinctive yellow barge. That platform sits approximately one mile from the Bayview facility, but beneath it is another remarkable number, 600 feet of water. Topic 10, the yellow barge over 600 feet of water. The Navy's yellow test barge operates where Lake Pend Oreille is roughly 600 feet deep. It supports calibration work, smaller models, and testing involving unmanned underwater vehicles. That depth alone demonstrates why the lake is so useful. Engineers can conduct deep water acoustic testing without traveling hundreds of miles offshore. Everything remains close to shore facilities. Personnel can return to the laboratory. Models can be recovered and modified. Tests can be repeated under similar conditions. And because the environment is quieter than many ocean locations, researchers can detect acoustic changes that might otherwise disappear into background noise. Sometimes the Navy goes even further to eliminate interference. Testing can happen at night. Topic 11, why tests sometimes happen at night. Even Lake Pend Oreille isn't perfectly silent. Recreational boats generate noise. Weather changes the water surface. Wind affects operations. Those sounds can contaminate acoustic measurements. The Navy says some testing is therefore conducted at night when conditions can be quieter and boat traffic is reduced. This reveals how sensitive the experiments can be. A passing recreational boat may create enough sound to interfere with measurements of a submarine model operating deep below. The facility isn't trying to produce spectacular explosions or dramatic underwater maneuvers. It's often trying to measure tiny differences in sound, and that requires an environment quiet enough for those differences to be detectable. But cutthroat isn't the only advanced submarine design represented beneath the lake. Topic 12, the Columbia-class model. In August 2022, Navy personnel recovered another submarine model from Lake Pend Oreille. Its name was Pike. Pike is a scaled model associated with the Columbia-class submarine, the Navy's next generation ballistic missile submarine program. Unlike cutthroat, Pike can remain deployed on the ISMS range for extended periods. The Navy says a typical underwater test can last between one and eight weeks. During that time, sensors continuously collect information. But engineers don't have to sit above Pike in a boat. The model is connected back to shore through a cable extending an extraordinary distance. Topic 13, the 14-mile fiber-optic connection. When Pike is deployed underwater, the Navy can control and monitor the experiment through approximately 14 miles of fiber-optic cable. Data from range sensors and onboard instruments flows back to the laboratory. Engineers can record measurements continuously. Once testing is finished, Pike is recovered and returned to the model engineering support facility. Its configuration can then be changed. Researchers analyze the previous test. Components can be modified. Then another experiment begins. That repeatability is one of Lake Pend Oreille's biggest advantages. The Navy can change one variable and measure what happens without the enormous cost of altering a full-sized operational submarine. The lake becomes a controlled bridge between small laboratory experiments and the real fleet. Topic 14, the Zumwalt connection. Submarines aren't the only naval designs tested here. Another vehicle called SeaJet is associated with surface ship research. The Navy describes SeaJet as a one-quarter scale model generally representative of the USS Zumwalt, DDG-1000. Its research has included radar cross-section and underwater electromagnetic testing. That means the Idaho facility isn't simply listening for submarine noise. It can investigate how different naval platforms interact with multiple detection systems. The connection is extraordinary. An advanced stealth-oriented destroyer designed to operate on the world's oceans has part of its research story tied to a mountain lake in Idaho. But there is a reason the Navy uses models instead of simply testing everything at full scale, money. Topic 15, why models save the Navy money. Full-scale submarine trials are enormously complicated. An operational submarine requires a crew. Support vessels may be necessary. Ocean test ranges cost money. Modifying a full-scale design can be extremely expensive. At Bayview, the Navy uses large models to occupy the middle ground between small laboratory models and full-size ships. According to the Acoustic Research Detachment, the models are large enough to reproduce important structural characteristics while remaining significantly cheaper than full-scale testing. NABC specifically credits past experiments at the site with supporting submarine propulsor design, sonar dome development, and construction cost avoidance. A design problem discovered in Idaho can therefore potentially be corrected before it becomes an enormously expensive problem on a real submarine. And some of those lessons travel thousands of miles from Idaho. Topic 16, the data leaves Idaho. Lake Pend Oreille provides the physical experiment, but much of the analysis connects back to West Bethesda, Maryland, home of Carderock Division. Data collected from models in Idaho is transferred for processing and used to answer questions about full-scale submarine platforms. That creates an unusual research chain. A submarine model operates beneath a mountain lake in Idaho. Hydrophones record its acoustic signature. Fiber optic systems transmit measurements. Engineers analyze the results. Then those results can influence real naval designs intended for the Atlantic, Pacific, and other oceans. Idaho may be hundreds of miles from saltwater, but the data collected there can ultimately affect submarines operating around the world. If you enjoy DiscoverTube investigations into places hiding something completely unexpected, subscribe, because the next part explains why this lake behaves more like an enormous controlled laboratory than a normal body of water. Topic 17, the water changes below 100 feet. One of Lake Pend Oreille's biggest scientific advantages begins approximately 100 feet beneath the surface. The Navy describes the deeper water as essentially isothermal, meaning its temperature becomes relatively uniform. Why does that matter? Sound underwater is strongly influenced by environmental conditions, including temperature. If those conditions vary dramatically, interpreting acoustic data becomes more difficult. A relatively stable deep water environment makes mathematical analysis cleaner. Combine that with a relatively flat bottom and low background noise, and researchers get something rare, a natural body of water behaving more like a controlled test tank, except this test tank is more than 1,100 feet deep and roughly 148 square miles across. Topic 18, a 25-acre facility beside the wilderness. The Acoustic Research Detachment itself occupies roughly 25 acres near Bayview, next to Farragut State Park. From the surrounding landscape, the contrast is extreme. Mountains, forests, cold, fresh water, recreational boats, wildlife, then beneath the surface, autonomous submarine models, acoustic arrays, underwater projectors, hydrophones, fiber optic cables, deep water ranges. The Navy says all acoustic testing is conducted under environmental guidance intended to avoid damage to the lake and its native species. The facility has also supported work involving private industry, academia, U.S. allies, and other defense organizations, but even the lake itself is not entirely natural anymore. Topic 19, the dam changed the lake. Lake Pend Oreille is now regulated by Albany Falls Dam as part of the Columbia River System. The dam supports downstream power generation and flood control. According to Idaho's state water planning records, before construction of the dam, the lake naturally fluctuated by approximately 13 to 14 feet between winter low water and spring high water. The dam altered those natural variations. But the deep basin itself is far older. Glaciers created the basic landscape thousands of years before the Navy arrived. That history produced the depth. The mountains created isolation. The lake's geometry created quiet water. And 20th century infrastructure made conditions even more controllable. In other words, almost everything about Lake Pend Oreille accidentally lined up to create an ideal underwater laboratory. Topic 20, what the Navy is actually hiding in plain sight. The strange part is that much of this isn't technically secret. The Navy publicly describes the facility. It has published photographs of Cutthroat. Pike has been photographed being lifted from the water. SeaJet has been identified. The 158 hydrophones, 36 projectors, 14 mile fiber optic cable, 1,680 batteries, and four test ranges have all been publicly discussed. What remains sensitive are the details that actually matter operationally. Exact performance, acoustic signatures, design improvements, how quiet specific submarine technologies can become. Those aren't numbers the public gets to see. And that's what makes Lake Pend Oreille fascinating. The giant underwater laboratory isn't hidden. Its most important results are. The final discovery. Lake Pend Oreille looks like remote Idaho wilderness. But put the numbers together. A lake covering roughly 148 square miles. Depth approaching 1,150 feet. A Navy research facility occupying 25 acres. Four major underwater ranges. 158 hydrophones. 36 acoustic projectors. A testing barge over 600 feet of water. A 14 mile fiber optic connection. A one third scale Virginia class submarine model powered by 1,680 lead acid batteries. And Columbia class research models that can remain underwater for up to eight weeks at a time. None of this exists in San Diego, Norfolk, Pearl Harbor, or another obvious naval port. It's in Bayview, Idaho, and the reason goes back thousands of years. Ice age glaciers carved a basin deep enough for modern submarine testing. World War II brought the Navy to its shore in 1942. More than 293,000 sailors trained nearby. Then researchers realized the lake offered something difficult to reproduce anywhere else. Deep, cold, quiet, and relatively controlled water. Today, technology developed and evaluated here can contribute to submarines that eventually operate thousands of miles away in the world's oceans. So here's the question. If this much of the Navy's Idaho operation is publicly known, what technologies are being tested beneath Lake Ponderay that we'll only learn about years from now? Tell us what you think in the comments below. And subscribe to Discover Tube for more investigations into America's most unexplored and unexpected places. Because one of America's most important submarine testing environments isn't hidden beneath the Pacific. It's more than a thousand feet deep in the mountains of Idaho.