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The U-111: The Elusive U-boat

Shipwreck explorer, historian, and author Gary Gentile recounts the extraordinary tale of the search for the elusive U-111 sub—the sole missing shipwreck out of the nine so-called Billy Mitchell wrecks that he and Ken Clayton located and dived in the 90s. It was a search that occupied the deep sea detective for more than 30 years. Despite preliminary pushback from skeptics, Gentile was proven right on June 22, 2022, when the lost sub was finally imaged and identified. Here is his story.



by Gary Gentile. Images courtesy of Gary Gentile unless noted.

The first time I heard about the U-111 was in 1989. I had just started conducting extensive research for two simultaneous projects: the search for the German battleship Ostfriesland and its associated shipwrecks (called the Billy Mitchell Wreck Project), and a book in my fledgling Popular Dive Guide Series titled Shipwrecks of Virginia. The timing was perfect because the Billy Mitchell Wrecks lay off the coast of Virginia.

After World War I, the U.S. Navy commandeered 11 warships from the German fleet: the battleship Ostfriesland, the cruiser Frankfurt, three destroyers (G-102, S-132, V-43), and 6 U-boats (U-111, U117, U-140, UB-88, UB-148, and UC-97). The Navy’s purpose was to study German naval construction and technology. In nearly every case, German warships were found to be more advanced than U.S. warships.

U-111 Conning Tower

In accordance with the Washington Naval Treaty—which limited the number of warships and the total tonnage that each nation was allowed to have in service—these warships had to be scuttled “beyond the 50 fathom curve” by July 1, 1921. During the interval between acquisition and the prescribed scuttling date, some of the U-boats were examined in detail by naval engineers, while others toured coastal cities for two reasons: to give curious citizens an opportunity to climb aboard a U-boat and walk through its interior, and to promote the Victory Bond Drive, in which citizens were encouraged to purchase war bonds in order to help get the United States out of the debt that had been incurred by the war with the Axis powers.

The UC-97 toured the Great Lakes, after which it was scuttled in Lake Michigan. The UB-88 toured the southern states, then passed through the Panama Canal and toured states along the West Coast; it was scuttled off San Pedro, California. The remaining warships were scheduled to be scuttled in a series of shipboard artillery and aerial bombing tests off Virginia.

A R-class Sub with the U-111 in the background.

Sinking of the U-111

The Billy Mitchell Wrecks Project was created and led by Ken Clayton and myself. Together we did an enormous amount of primary research, not only historical but also gaseous—we had to breathe heliox and trimix because of the extreme depths. Between 1990 and 1995, we found and dived on eight of the nine so-called Billy Mitchell Wrecks: all. . . except for the U-111.

This came as no surprise to us, for in 1989 we had already learned from archival research that the U-111 had not been scuttled with the other Billy Mitchell Wrecks, this because it had already sunk—prematurely, accidentally, of its own accord, and to everyone’s grief—a week before the tests were scheduled to commence.

To backtrack from the disaster described above, after reaching the American coast, the U-111 first participated in the Victory Bond Drive by visiting ports along the New England coast. It then underwent a series of performance tests in which the U-111 outperformed American subs. It was subsequently laid-up at the Portsmouth Navy Yard in New Hampshire.

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When it came time for the ultimate test in which the U-111 was to be either shelled or bombed to destruction, it hitched a ride behind the minesweeper Quail. During the 600-mile tow, sailors noticed that the hull kept settling by the head. By the time the vessels reached the Chesapeake Bay, the bow was down by about 4 feet. The U-boat was secured to a piling. A quick inspection of the interior found that the torpedo room was filled with water. The Quail stood by the U-boat overnight while a pump dewatered the compartment. Two hull plugs blew out in the morning, causing the U-boat to settle alarmingly.

Sailors quickly re-rigged the towing lines. The Quail towed the U-boat toward shallow water in an attempt to beach it. The U-boat came to a sudden stop when the bow struck sand and grounded in 5 fathoms/10 m/30 ft of water. And there it stayed. For a year.

The date was June 18, 1921. The scuttling date was four days later. The only salvage vessel in the area was the Falcon. At that time, the Falcon had been working on the salvage of the U.S. submarine S-5 for nearly a year. Not until the submarine was raised or abandoned would the Falcon be available.
Because the U-boat’s conning tower was exposed and liable to collision, a gas buoy with a red flashing light was placed on the wreck. Six mooring buoys were deployed. Salvage of the S-5 was terminated, and the wreck was abandoned. The Falcon arrived at the site of the U-111 on October 1. After a month and a half of hard work, the Falcon was assigned to other duties. She wintered in New York where she underwent a refit. Not until June 1922 did the Falcon return to the sunken U-boat.

U-111 Interior.

Raising the U-111

Divers found an open torpedo door and were able to seal it. They also replaced the wooden plugs that had popped out of the pressure hull. On July 29, the Falcon pumped air into the U-boat’s compartments, but succeeded in raising only the stern. On August 4, she towed two pontoons to the wreck site. After much work attaching the pontoons to the sunken hulk, the U-111 was successfully raised and towed to dry-dock at the Norfolk Navy Yard. The battered U-boat was repaired well enough so it could be towed to sea and scuttled.

On August 30, the Falcon proceeded for the Portsmouth Navy Yard with the U-111 lashed to her starboard side. Aboard the salvage vessel was one Mr. H. D. Blaunet of the Pathe Moving Picture Company, who was assigned the task of photographing the U-boat’s final event. Once in the open sea, the U-boat was towed astern on 100 fathoms/183 m/600 ft of wire. The following day, when the Falcon reached the pre-arranged scuttling site, a charge was detonated in the forward battery room. The detonation blew a hole in the pressure hull. Another charge was set in the aft torpedo compartment.

U-111 Conning Tower

According to the Falcon’s deck log, which I located in the National Archives in Washington, DC, the U-111 sank stern-first in 266 fathoms/486 m/1,596 ft. The coordinates of the scuttling site were also noted in the deck log: 37°45’15” N / 74°07’45” W (or thereabouts, for in those days the only way to determine a position at sea, out of sight of land, was by sextant, chronometer, and a book of mathematical tables).The crew would have taken a sun sighting either at sunrise, noon, or sunset; or a night sighting of the North Star (Polaris), then by dead reckoning: a system of extrapolating the distance and direction traveled from the vessel’s speed, the direction and speed of the water’s drift, and wind’s direction and speed.

When I plotted the coordinates on a chart, I noticed an anomaly: the depth of water at the given latitude and longitude did not correspond with the depth that was recorded in the log; it was shallower by hundreds of feet. So, was the position correct, or was the depth correct? Or neither?

Thirty years passed before I learned the truth.

Sidescan sonar image taken by Ben Roberts

Finding the U-111

In 2018, my friend Ted Green sent me the coordinates of a commercial fishing site called the Olinda Wreck, believing that it was the remains of a freighter that was torpedoed during World War II. This seemed unlikely in that historical sources placed the Olinda at least 48 km/30 miles from that location. The wreck lay on the edge of the Continental Shelf at a depth of 119 m/390 feet.

When I marked the GPS numbers on my old chart, I saw that the wreck lay only 5.6 km/3.5 miles from the U-111. I thought that was an interesting coincidence. There are so many shipwrecks off the eastern seaboard that there are bound to be wrecks that lie close to other wrecks. For example, popular dive sites Chaparra and San Saba lie only a mile apart. To me, they and the U-111/Olinda represented little more than a curiosity.

A year or so later, Green gave the Olinda Wreck location to Joe Mazraani. In December of 2020, when Mazraani side-scanned the Olinda Wreck, he found that the wreck was not a freighter but a submarine, which he identified as the R-8. The R-8 had been scuttled in a bombing test in 1936. Except for a photograph in my R-8 folder, the only information I had were its historical location and depth: some 113 km/70 miles from the Olinda Wreck, at a depth of 1,317 m/4,320 ft.

Charted positions!

Mazraani issued a press release including the side-scan sonar image. The conning tower in the scan did not look like the conning tower of the R-8. I pulled Shipwrecks of Virginia off the shelf and turned to the chapter about the U-111. The book had two photos of the U-111 and its conning tower. The conning tower in those photos matched the size and shape of the conning tower in the side-scan sonar image, and did not match the size and shape of the conning tower of the R-8. At that moment, I was certain that the Olinda Wreck was the U-111. And I remained fully confident in that conclusion.

However, no one believed me. For a year, I stood alone in my never-shaken confidence. Then it took another six months to obtain absolute proof—a year and a half in all.

Divers who had no background knowledge of the U-111 would not accept the results of my research. To them, yet another U-boat coming to light seemed preposterous. So little faith did Ben Roberts have in my conclusion that he decided not to side-scan the Olinda Wreck during his 2021 wreck survey, when he side-scanned 191 other wrecks! (See his website at Eastern Search & Survey)

U-111 conning tower. Photo by Ross Baxter.

Yet, not only was Roberts the first one to side with me after he corroborated my original research, but he also took matters in hand by convincing Ross Baxter to explore the wreck with his remotely operated vehicle and video camera. I must also mention those who subsidized the cost of chartering a boat by each donating $375 to the cause: John Copeland, Jon Haws, Michael Haws, Dan Quinlan, and Jim Walsh. I thank them all for the faith that they had in me and my promise to expose yet another lost U-boat to the world.

The confirmation dive took place on June 22, 2022. Afterward, Ben Roberts took his boat to the site and obtained high resolution side-scan images of the U-111. He annotated one image to show the most prominent features of the wreck.

As the saying goes: the rest is history.

This concise introduction to the emergence of the U-111 is told with greater detail in U-111 Exposed. The 240-page book provides information about the Billy Mitchell Wreck Project, focusing on the discovery of the other three U-boats. The book is illustrated with 90 photographs of the U-111, many of them showing the interior, plus another 82 black and white photos and 39 color photos. The book is available now.


The rest of the U-111 story from the U-111 Team: U-111 Teamwork, Technology and Wreck Identification by Rusty Cassway

The Rest of the story from the U-111 Team: U-111 Teamwork, Technology and Wreck Identification by Rusty Cassway

InDEPTH: For Whom The Shipwreck Bell Tolls by Gary Gentile


ScubaBoard: Neox, Argox, Ken Clayton & Billy Mitchell Fleet talk Our World Underwater Chicago (FEB 2017)

Gary Gentile Productions: The U-111 Exposed

Gary Gentile, author, lecturer, photographer, explorer, and deep-sea wreck-diver, has written 68 books—including one of the first on technical diving—published more than 4,000 photographs, and discovered more than 40 shipwrecks. He was the first scuba diver to enter the First Class Dining Room of the Andrea Doria, and he recovered a number of Italian artist Romano Rui’s ceramic panels that once adorned the walls of the First Class Bar. 

In the early 1990s, he was instrumental in merging mixed-gas diving technology with wreck diving. His dive to the German battleship Ostfriesland, which lies at a depth of 116 m/380 ft, triggered an expansion in the exploration of deep-water shipwrecks and the advent of helium mixes. 

Gary specializes in wreck diving and shipwreck research, concentrating his efforts on wrecks along the eastern seaboard from Newfoundland to Key West and in the Great Lakes. Over the years, he has recovered many thousands of shipwreck artifacts. He has preserved and restored these relics from the deep and displayed them at various museums, symposiums, and exhibitions.

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Laying Line in Cozumel

While tech divers thrill in the joys of mixed gas, reef drift diving, Rob Neto and his team continue to plumb the Cozumel underground, emptying their reels in newly discovered La Sección Escondido, la Cueva Quebrada, Aerolito, and a newly discovered cave that they’re keeping to themselves for now. Neto says there are tens of thousands of kilometers of passageway left to go! We also include a look at the Cozumel Underground nearly 30 years ago. Dive in!




by Rob Neto. Images courtesy of Laurent Miroult unless noted. Lead image: The author posing next to a large silt covered dripstone formation just below the halocline in la Sección Escondido.

A blast from the past! Check out the state of Cozumel caves more than 30 years ago. COZUMEL UNDERGROUND by Michael Menduno

Swimming through a passage large enough to drive a bus through with plenty of room to spare, I’m balancing my speed against my breathing rate. I could move faster, but that would only cause me to have to turn sooner, and I definitely don’t want to do that. I also still have to survey on the way out. It’s one of my rules for exploration – never lay more line than I can survey on the exit. Of course, there are exceptions, as with every rule. But none of them apply at the moment.

I’m laying line from my second exploration reel. Yep, number two, on that dive! There’s so much virgin passage it’s almost overwhelming. Each reel carries about 335 m/1100 ft of line. And the one in my hand, the second one, is almost empty. I can see a wall at the end of the passage, but the passage looks like it turns to the right. I think I should have enough line to make it a little beyond that turn. I’ll have to return to keep pushing the passage. As I approach the wall, I see what looks like an old cave line lying on the floor. I’m still too far from it to know for certain.

This is a saltwater cave, which means there is more life here than is found in the freshwater caves. So what I was seeing could be some sort of biological material. As I get closer, I notice what resembles a Dorf marker (named after Lewis Holzendorf who came up with the idea), the old duct tape line arrows that were common back in the 80s and 90s. My shoulders drop. The exploration of this passage has come to an end.

When most divers think of Cozumel, they think coral reefs and drift diving. Little do they know Cozumel, like Riviera Maya just across the channel, is home to numerous caves and the site of active exploration. 

Finding Cenote Escondido

On that dive alone, I laid more than 600 meters/2000 feet of line. That’s in addition to more than 6000 meters/20,000 feet of line in that section since I first found it in 2015. The lead I found at that time brought me through a small bottle off sidemount restriction. It wasn’t a long traverse through the restriction, maybe ten feet. And once on the other side, the passage got wide and tall and went for miles/kilometers.

Along the way, about 450 m/1500 ft from the restriction, I found a cenote during a subsequent trip. Somehow, I had missed it when I first lined the passage. I guess I was so focused on pushing the passage I didn’t notice the debris, evidence of a cenote overhead, and the opening was small enough that a little rain produced sufficient tannins to darken the opening that day, so there was no daylight falling into the passage my first time through it. This time we were there during the dry season and daylight was penetrating the depths.

Broken stalagmite found in la Sección Escondido. This is one of many such formations in that section.

As I approached it, I saw the light ahead and thought to myself, who else could be down here in this cave? Then I realized it wasn’t the light from a diver, but the light from an opening that I was seeing. That’s when I noticed the leaves and tree branches strewn about on the floor of the passage. I covered my light and signaled to my buddy, Laurent Miroult (whose photos accompany this article). We stopped and I tied in a jump spool so we could surface. It was only 4.5 m/15 ft deep at this point. We surfaced in a small cenote that would fit one additional diver, as long as the three of us were very comfortable with each other. 

The surface of the water was about 2 m/6 ft below the jungle’s floor. And there were no footholds to assist in getting in or out of this cenote. There was also no shelf to set our tanks on while we tried to climb out. We’d have to find this from the surface another time. We descended back into the cave and I did a quick survey, three stations each way, so I could pinpoint the location of the cenote on my map. I already had a name chosen for it – Cenote Escondido (Hidden Cenote). Laurent and I went back the next day to surface again while another team member searched the area from above. It took us about an hour to swim to the cenote from our entry point, so we coordinated the times and began our journey.

A little over an hour later we surfaced in Cenote Escondido and began yelling out for our teammate. About 15 minutes later, we heard him yelling back. It took him another 15-20 minutes to hack a path through the dense jungle to get to us. The cenote was even more hidden from above! He finally arrived, tired and sweaty, scratched up and bruised. He also had news of another cenote he had found as he was hacking his way through the jungle to the approximate waypoint derived by my survey (it’s since been named Cenote Catedral because of its cathedral-like appearance). 

Now we had a waypoint, and we could form a direct path through the jungle to Cenote Escondido. This would allow us to cut an hour of swim time from our dives. We cut the path through the jungle, but we would need to hold off on beginning our dives at the new cenote until the next trip because we needed ropes and ladders to get to and from the water’s surface and to secure our cylinders at the surface.

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Back to Cenote Escondido

Immediately upon returning to Cozumel a few months later we headed straight to Cenote Escondido and set up our equipment ropes and a couple of rope ladders we had brought with us to the island. Over the course of the next three days, I laid about 1700 m/5500 ft of line using that cenote as the starting point. Not only did entering through Cenote Escondido cut an hour of travel off the dive but it also put us right in the center of a cave explorer’s dream come true. Within 10 minutes of descending below the surface, we were laying line in virgin passage. This happened all three days! The last day was the day I finally looped back to the 35-year-old line with the old Dorf marker on it.

I follow the old line for about 45 m/150 ft before coming to an intersection that looks very familiar. In fact, it looks so familiar I am 99% sure where I am in the cave. I turn around and survey on the way out. That evening, back at the hacienda, I plot out my data and I end up right where I thought I was – only a 15-minute swim from another cenote we had accessed many times before. One of my previous team members had surveyed this area of the cave a couple of years prior. I had been to the intersection I recognized but didn’t go beyond it. Lesson learned – don’t just accept survey data from team members; go look at it for yourself!

So, two cave divers had both been to the end of the line, the one with the Dorf marker on it, and missed the larger-than-a-bus passage to the left of where it ended. I have to say I was very thankful for that because, had they noticed it, the passage wouldn’t have been there for me to discover and explore. Ok, so, yes, I found it from another location more than 900 m/3000 ft away as the fish swims. I aptly named the section that had been missed by at least two other divers la Sección Escondido, after the cenote.

Rob caught looking up at the newly discovered Cenote Escondido.

La Sección Escondido currently measures approximately 10,500 m/35,000 ft in length. That’s 1900 m/6000 ft longer than the known extent of la Cueva Quebrada at the time of the original exploration and map. My team and I have laid much more line than that in other sections of Quebrada. This includes the connection between la Quebrada and Dos Coronas, which is now la Sección Dos Coronas of la Cueva Quebrada. See the article describing the connection we made in 2014.

Our explorations, along with explorations made by Steve and Judy Ormeroid in the late 2000s/early 2010s has resulted in la Cueva Quebrada currently measuring approximately 26,000 m/85,000 ft of lined and surveyed passage. And I’m not done yet. We still have ongoing exploration that we are certain will push the length of the system well over 30,000 m/100,000 ft. This makes la Cueva Quebrada the longest underwater cave system on the island of Cozumel and places it in the top ten for all underwater caves in Mexico. Our future explorations will go a bit easier because we now have DPVs on the island to facilitate travel time to the areas we are currently exploring.

Rob preparing to explore a new lead in laSección Escondid.

Exploring Aerolito

In addition to our exploration in la Cueva Quebrada, we have also been resurveying and exploring Aerolito de Paraiso, the only cave on Cozumel that is publicly accessible. The original map of Aerolito reported 6000 m/20,000 ft of passage. Our explorations have increased that number to more than 7900 m/26,000 ft of lined passage as of 15 AUG 2023. And we are also still actively exploring Aerolitol. In fact, we are hopeful that we will be able to connect Aerolito to another cave on the island that we have been exploring.

This other cave was completely virgin prior to us finding it. There’s more than 940 m/3100 ft of line in that cave and the ongoing passage appears to be heading straight for Aerolito. There’s still some distance to be covered between the two caves, but we have located a possible access point along the way that we may use at some point. The island caves never stop surprising us. 

The last couple of days haven’t provided quite the honeypot of virgin passage that we experienced at the beginning of the week. We might finally be nearing the end of our exploration efforts. 

Rob laying line in a newly found passage in la Sección Escondido.

That’s been the thought on a few of the early trips to Cozumel in the past. I stopped having those thoughts long ago. I always have a knack for finding ongoing passage on the last dive of the trip. I even ran out of line on one of the early trips! Now I have an excess of line on the island. I’ll always have enough for at least two trips of diving. And the thoughts that I’ll ever be done exploring the passages that lie under the jungle are long gone. I’m certain I’ll be retiring from exploration and passing the reins to a younger generation before it’s fully explored. I’m already mentoring someone for that responsibility and honor. 

In the meantime, I schedule the next trip before I even leave to return home from the trip I’m on. And anxious to get back to continue pushing the lead I found earlier in the day. Unfortunately, COVID slowed things down for a couple of years, but with that mess mostly behind us, we are now back strong and pushing the leads regularly again. I’m looking forward to when I can make the announcement that we’ve busted the 30,000 m/100,000 ft mark.

Cozumel Underground

Thirty years ago, no one believed that Cozumel had caves. They were wrong. Here’s a brief dive into the Cozumel underground circa 1997.

Dive in


YouTube: Aerolito de Paraiso  by Rob Neto

Cozumel Caves: Cozumel’s Influence in Choosing a Sidemount Rig (2014) by Rob Neto

InDEPTH: Deep Drift Diving in Cozumel by Alberto Nava (2019)

InDEPTH: The Who’s Who of Sidemount: Rob Neto

Speaking Sidemount E062 – Rob Neto – The Almost Comprehensive Guide to Sidemount

BOOKS:Check out Neto’s debut novel: Beyond the Grate Sidemount Diving: The Almost Comprehensive Guide 2nd edition

Rob Neto is an experienced cave diver, explorer, and surveyor. He has been diving and exploring caves for 20 years and was a dive instructor for over 10 years. His current focus in diving is cave exploration and mapping, as well as traveling around the world to experience caves everywhere. When not exploring Rob focuses on documenting underwater caves with video and as a photography model. He has been cave diving in several countries and has ongoing exploration projects in the US, Mexico, and France, as well as assisting with a project in Italy. He primarily dives sidemount configuration due to the nature of his dives but also dives SCRs and CCRs when appropriate. Rob is the author of Sidemount Diving – The Almost Comprehensive Guide 2nd edition, as well as Beyond the Grate, a suspense thriller inspired by true events surrounding the disappearance of a diver last seen at a Florida panhandle spring where an underwater cave is located. He’s currently working on a sequel, Into the Darkness Beyond.

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