By Sven Röbel
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.
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.
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.
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
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