The tower was the first thing Jim Delgado saw. Inch by inch, it emerged from the deep-green surf of the Pacific Ocean -- an encrusted piece of black metal covered with barnacles, rust and seaweed, a ghostly apparition slowly rising from the sea.

Low tide came slowly and sluggishly, eventually exposing the mysterious rust-eaten wreck a fisherman had described to Delgado. The man believed it was a Japanese submarine that had been on a mission to attack ships near the Panama Canal during World War II, only to fall prey to the treacherous waters of the Pearl Archipelago.

But the more the tide retreated, the more Delgado -- director of the renowned Vancouver Maritime Museum -- was convinced that the fisherman's story couldn't possibly be true. This thing appearing before his eyes had to be older, much older.

The design reminded the scientist of an "iron cigar," and he instinctively thought of the "Nautilus," that legendary underwater vessel author Jules Verne described in his novel "20,000 Leagues Under the Sea." Delgado had devoured the book as a young boy.

But could something like this be possible? Delgado was mesmerized. Years ago, working as a marine archaeologist, he had recovered the wreck of the "General Harrison," a ship from the days of the California gold rush, from San Francisco Bay. He was also involved in the raising of the "H.L. Hunley" from the harbor entrance at Charleston, South Carolina -- the first submarine ever to sink an enemy ship, during the American Civil War in 1864.

And now, on this isolated beach on a tropical island -- during his vacation, no less -- he had apparently happened upon the most spectacular find of his career.

Without any equipment, and wearing nothing but boxer shorts, Delgado swam out to the mysterious wreck. He cursed when he scraped his left leg on the sharp-edged metal -- and because he didn't have a measuring tape to document the object's exact dimensions. The size, shape and condition of the chambers corresponded to none of the vessels he was familiar with -- and Delgado thought he knew just about everything that had ever floated. But this craft's technology seemed much more modern that that of the "Hunley." The shape of the hull was more reminiscent of the fantasy forms he'd seen in old science fiction books. Why on earth, he wondered, had he never heard about this vessel?

When Delgado heard the sound of the approaching rubber dinghy that had come to take him back to his cruise ship, he quickly took a few shots with his camera -- hardly able to believe his luck at having decided to pass on the dull bird-watching outing the other passengers had taken. His few hours on this remote island had truly been worth it.

Historic find

That was five years ago, and by now it's become clear that Delgado made a sensational historic find. He discovered the lost "Sub Marine Explorer," one of the world's first functioning underwater boats, designed by a brilliant German engineer whose invention eventually brought him an agonizing death.

The San Telmo discovery could provide answers to many questions about the first submarines. Some of Delgado's colleagues believe that the wreck in the Pacific is a unique example of a handful of submarine prototypes that have remained preserved. They are craft in which daring men -- essentially the Space Shuttle pilots of their age -- ventured into the unknown world beneath the ocean's surface in the 19th century. Only five diving machines from the years before 1870 have survived the ravages of time:

The "Explorer" marks a high point in maritime engineering, but also a tragic one. Equipped with a cleverly designed system of ballast chambers and a compressed air tank that allowed for pressure compensation, it also had two hatches beneath the hull enabling divers to exit the craft underwater. But about 130 years ago, when the vessel was being used to collect oysters and pearls from the ocean floor off the coast of Panama, the condition known as "the bends," or decompression sickness, was largely unknown. The condition can cause an agonizing death when divers rise to the surface from deep water too quickly. Technical progress had fatally outpaced medical science, costing the inventor and team of the "Explorer" their health and their lives.

But on the evening following his discovery, as he sat excitedly in the dining room of his cruise ship, Delgado had no idea of the tragedies that must have transpired in this iron coffin in the Pacific's pearl beds. Instead, he couldn't stop describing the details of the strange wreck to his wife Ann.

Back home in Vancouver, the scientist had the pictures he took on San Telmo developed and promptly e-mailed the images -- together with a description and a request for further information -- to colleagues around the world.

One man, Richard Wills, an expert on American Civil War submarines, wrote back to inform Delgado that his data were a perfect match to a description Wills had discovered in a scientific article from 1902. The piece even included a precise drawing of the largely unknown diving device. This couldn't possibly be a coincidence -- the vessel had to be the "Sub Marine Explorer."

Little known inventor

Little was known at the time about the man who designed the craft, a German inventor named Julius H. Kroehl who had emigrated to the United States. He built an iron fire watchtower in Harlem in 1865 and was then hired by the New York magistrate to demolish -- unsuccessfully, as it turned out -- a reef that obstructed shipping in the East River. But how did the mysterious German hit upon the idea of designing such a progressive diving ship? Delgado decided to get to the bottom of the story. A search through historical archives revealed that the "Sub Marine Explorer" last belonged to an outfit called the Pacific Pearl Company, which planned to dig for oysters off the coast of Panama in the 1860s.

 As far back as the days of the Conquistadors, divers had been digging up treasures from the depths of the "Archipiélago de las Perlas." Black slaves had once fished the famed "La Peregrina" pearl -- a magnificent, softly shimmering 50-carat jewel -- from the waters of the archipelago. The shells also held the promise of fortune, offering wealth in the form of mother-of-pearl, a highly sought-after luxury material used in the fashion of the day.

According to old business records, one of the partners in the company with offices near New York's Wall Street was a certain W.H. Tiffany, apparently a member of the eponymous jewelry and lamp dynasty.

The story was becoming more and more fascinating, and after making two more trips to San Telmo in 2002 and 2004, Delgado had finally collected enough material to justify launching an expedition to delve into the final secrets of the "Explorer" and its inventor.

Accompanied by SPIEGEL, an international team of scientists set out for the waters of the Pearl Archipelago on February 18. According to expedition leader Delgado, he had "assembled the best people" -- people like Australian Michael McCarthy, 58, a world-renowned underwater archaeologist, Larry Murphy, also 58, a specialist in corrosion studies, and metallurgist Don Johnson, 79, a proven expert in the study of materials and rust processes. One of the most pressing issues for the team was to determine how much longer the rare wreck would withstand constantly being submerged in salt water. They also wanted to find out what materials were used to build the craft and how it actually worked.

Armed with GPS navigation gear, multi-parameter probes and laser-guided distance measuring devices, the researchers tackled the archaic technology of the 19th century. "It was as if we were looking through a portal into a forgotten era," Delgado raves. He and his team found themselves constantly surprised by the ship's design and its technical intricacies.

The upper half of the ship's double hull, which once housed the compressed air tank, was made of pressure-resistant cast iron, while the lower half consisted of wrought-iron plates connected with rivets. The heads of the rivets were on the inside of the hull, apparently in an effort to make the boat, which was moved by a propeller driven by muscle power, as streamlined as possible.

In the fine layer of sand that covered the floor of the work chamber, with its two hatches for recovering oysters, Delgado found a depth gauge filled with mercury and the wooden handle of a manual pump, which was apparently used to improve the air in the small enclosed space. Spraying a fine water vapor was meant to bind the carbon dioxide in the air onboard the vessel. After all, the boat contained up to six men collecting oysters in candlelight, in what amounted to hard labor on the ocean floor.

All of these characteristics closely matched an old newspaper article Delgado's research assistants had previously dug up in archives. In the summer of 1869, the "Mercantile Chronicle," a Panama paper, using the florid language of the day, described how the revolutionary submarine worked. "Before submersion," wrote the paper, "enough air is filled into the compressed air chamber," using a "pump with the power of 30 horses" mounted on another boat, "until the air in the chamber reaches a density of more than 60 pounds," which corresponds to pressure of about four bars. Once the compressed air tank has been sealed, "the men enter the machine through the tower on the upper side" and "as soon as the water is permitted to fill the ballast chambers, the machine sinks directly down to the ocean floor," where "a sufficient amount of compressed air is promptly fed into the working chamber until it possesses sufficient volume and power to resist the enormous pressure of the water," so that the men can "open the hatches in the floor of the machine" and begin recovering oysters.

The writer continued: "When they have been underwater for a sufficient period of time and all shells within reach have been collected," compressed air is pumped into the ballast chamber "and as this air then forces out the water, the machine safely rises to the surface."

Ignorant of diving dangers

Kroehl, the designer, couldn't know how important gradual, controlled pressure compensation is during surfacing. Nowadays, when underwater researcher Delgado, himself a practiced diver, climbs into the narrow chamber -- bathed in a pale, green light from the midday tropical sun -- he surveys the rust-covered valves, rudder levers and handles and tries to imagine what it must have felt to work "in this iron coffin." What it must have been like to hear the hissing of compressed air with ears aching from the pressure, and how sour the air must have smelled when almost all the oxygen had been consumed and the candles were slowly being flicker out.

Delgado waxes philosophical at such moments and talks about the "great flow of history that extinguishes the individual." He has been studying the "Explorer" for five years now, and yet he doesn't even know what its inventor looked like. Although Kroehl himself was said to have been a passionate photographer, not a single portrait of the man has been found.

The biography of the forgotten engineer, compiled from the rudimentary recollections of his descendants and the records of his military service with the Union army, is still filled with gaps. Kroehl was born in 1820 in the East Prussian town of Memel, now Klaipeda in Lithuania, and as a child moved with his family to Berlin. Old address books reveal that his father, businessman Jacob Kröhl, lived at Hausvogteiplatz 11 between 1829 and 1833.

In 1838, after having served in an artillery unit in the German military, the young Julius apparently boarded one of the many emigrant ships that were then taking countless Germans to the shores of the New World. American records show that Kroehl became a US citizen in 1840. New York City commercial records from 1855 list him as an engineer in Lower Manhattan, an area filled with docks, iron foundries and plenty of German immigrants.

By then, Kroehl had filed a patent for the "Improvement of iron-bending machines," and he was apparently fascinated by the diving bells that had recently been developed for use in bridge construction.

In November 1858, Kroehl married 26-year-old Sophia Leuber in Washington, and beginning in 1863 he spent a year and a half fighting in the American Civil War. He served in the Union navy as an underwater explosives specialist and later as a scout in the Louisiana swamps. There Kroehl apparently contracted an illness that kept him bedridden for months. Between bouts of fever, the inventor must have repeatedly worked on the idea for his underwater machine. His thoughts probably revolved around a sort of diving bell, but one that was self-propelled and able to move freely -- and could therefore be used to attach mines to enemy warships.

But by the time he had finished the plans and regained his strength, the navy was less than enthusiastic. The war was over and Kroehl's project was too costly. The military simply failed to recognize the enormous potential of this type of submersible battle machine. Attempts with a few other devices had been less than encouraging, but Kroehl's submarine was technically superior to everything that had preceded it.

Refusing to give up, the inventor in 1864 became chief engineer and a partner in the Pacific Pearl Company -- a company that made headlines two years later. In the spring of 1866, the New York Times reported on the first sensational dive of the "Sub Marine Explorer." On May 30, at about 1:30 p.m., Kroehl, accompanied by three friends, entered his underwater device and dove to the bottom of the harbor at North Third Street. Bystanders spent an hour and a half waiting anxiously before the steel monster reappeared at the surface and the hatch slowly opened. Kroehl, clearly in the best of spirits, casually puffed away at his meerschaum pipe and proudly presented a bucket of mud, freshly collected from the bottom of the harbor.

The Pacific Pearl Company's investors were apparently impressed by the demonstration. That same year, they paid to have the disassembled "Explorer" shipped from New York to Panama's Caribbean coast, where it was loaded onto a train and taken through the jungle to Panama City on the Pacific. At the time, the town was a mosquito-infested pit, full of shady bars, corrupt officials and feverish fortune-hunters en route to California -- a way station on the new transit route between New York and San Francisco.

Arrival in Panama

On December 8, 1866, the news of the arrival of an incredible diving apparatus caused a sensation in the chaotic city. The device was apparently being assembled at the train station and would soon be ready for use. About six months later, the "Panama Star and Herald" reported that the work was finally complete. Engineer Kroehl, the paper wrote, had personally supervised the hoisting of the "Sub Marine Explorer" into the adjacent dock, and in a few days the boat would begin its first diving trips off the coast of islands owned by the Pacific Mail Steamship Company.

The trial runs, which lasted several weeks, apparently proved to be Kroehl's undoing. Completely confident in his invention and obsessed by the possibilities of working deep underwater, he couldn't possibly know that nitrogen molecules expand into small gas bubbles in the body when a person surfaces too quickly, essentially causing the blood to foam.

When Julius H. Kroehl died, on Sept. 9, 1867, doctors made the usual local diagnosis and the US consul made it official, writing to Kroehl's widow that her husband had died of "fever." None of them could have known about the deadly decompression sickness. The funeral, the consul wrote, was held by the local chapter of the brotherhood of Freemasons at the "Cementerio de Extranjeros," or Foreigners' Cemetery, in Panama City's Chorrillo district.

For two years after Kroehl's death, there were no further reports of the "Explorer," until the New York Times published a story about a pearl diving expedition to an island it called "St. Elmo." On an August day in 1869, at about 11 a.m., the boat apparently dove down into the waters off Pearl Island, remained submerged for four hours and finally surfaced with 1,800 oysters on board. The process was repeated on each of the next 11 days, until the crew had collected 10.5 tons of oysters and pearls worth $2,000.

But then, wrote the paper, "all divers succumbed to fever," which ultimately led to the undertaking being abandoned. The devilish machine, according to the Times, was taken to a protected bay off the island, where the crew soon planned to return -- but this time with "local, acclimated divers" supposedly immune to the "fever."

It was in precisely this bay, in the green waters off San Telmo, that Jim Delgado found the "Explorer" surfacing at low tide, as it has been doing every day for the past 137 years.

Translated from German by Christopher Sultan