The invention of the pearl diving submarine turned into a disaster

Inventor Julius Hermann Kroehl's submarine made pearl diving less laborious but also led to the deaths of many divers.

In 1863, German-American inventor and engineer Julius Hermann Kroehl founded the Pacific Pearl Company with the goal of profitably exploiting pearls in this sea. To ease this labor-intensive process, he began building a specially designed submarine to assist in collecting oysters and clams, according to Amusing Planet .

Pearl diving relies entirely on divers working without breathing apparatus. These divers descend to depths of 6-12m, collecting as many shells as they can before surfacing, often holding their breath for up to a minute. The work takes place during low tide, allowing access to deeper areas of the seabed. However, the dives are short, lasting only 2-3 hours. In the limited time frame, divers make 12-15 dives to the seabed. Recognizing the risks and inefficiencies of this method, Kroehl sought to revolutionize the process, taking divers out of unnecessary danger while improving productivity.

The wreck of the Sub Marine Explorer in 2006. (Photo: James P. Delgado).

Kroehl's Sub Marine Explorer was 11 meters long and 3 meters in diameter, weighing 80 tons. Its complex design included three separate sections: a pressurized air chamber under the upper hull, a central working chamber for the crew, and a series of 10 ballast tanks. To dive, a steam-powered refueling vessel pumped air into the high-pressure chamber at 13.6 atmospheres. After filling the chamber, Kroehl and his team opened a valve on the ship's main control station and flooded the ballast tanks to sink the submarine. As water rushed in, the air it displaced poured into a series of exhaust pipes leading to a manifold, then out through a valve in the conning tower. Kroehl steered the submarine by controlling the flooding and relied on pressurized air to push seawater out of the ballast tanks.

Once the submarine is underwater, pressurized air is released into the working chamber until the internal pressure equalizes with the pressure of the surrounding ocean. At this point, the hatch at the bottom of the submarine can be opened without letting water in. With the air inside the working chamber completely waterproof, divers can climb out to collect the pearls.

To generate thrust, the Sub Marine Explorer uses a hand-cranked thruster that can reach speeds of 7.4 km/h. In addition, the air inside the vessel is renewed by spraying seawater through a chemical compound, maintaining breathing conditions during long dives. To surface, more pressurized air is pumped into the ballast tank to push water out.

The Sub Marine Explorer made several successful dives off the coast of Panama, demonstrating the potential of submarine technology for pearl diving. In particular, on one dive, the crew collected 1,800 clams, weighing nearly 900kg in just 4 hours. However, after 11 days of searching for clams, the entire crew fell ill with fevers for unknown reasons, and some died shortly thereafter. Some local accounts said that these deaths occurred after diving for many hours at depths of over 30m and surfacing quickly.

At the time, Kroehl and his crew did not fully understand that the cause of the tragedy was decompression sickness . The condition results from the physiological effects of breathing pressurized air underwater. When a diver goes underwater, the increased pressure forces gases such as nitrogen to dissolve into the blood and tissues. If the diver ascends too quickly, the sudden drop in pressure causes nitrogen to form bubbles inside the body, leading to a variety of symptoms.

The effects of decompression sickness range from mild joint pain and rashes to more severe consequences such as paralysis or even death. Nitrogen bubbles often collect in vital joints such as the knees or wrists, forcing victims to bend over in pain. Kroehl and his crew did not know that they would need to ascend slowly and in controlled conditions to avoid life-threatening complications.

Kroehl died in September 1867 of a fever, although there was widespread speculation that his death was related to decompression sickness during his experimental dives with the Sub Marine Explorer. His wife dismissed this theory and suggested that he died of malaria contracted while serving in the Vicksburg campaign.

Without Kroehl's leadership and the financial resources to sustain operations, the Pacific Pearl Company ceased operations. The crew returned to New York, abandoning the Sub Marine Explorer, which ran aground. In 1869, another crew refurbished the ship and brought it back to the Pearl Islands to resume harvesting oyster shells and pearls. However, the deep dives left many divers sick or dead. Repeated tragedies forced them to abandon ship in a cave on San Telmo Island.

For decades, the ship's rusty hull intrigued local residents. In the early 2000s, James P. Delgado, an archaeologist with the American Institute of Maritime Archaeology, rediscovered the 19th-century ship. Despite the interest in the Sub Marine Explorer, efforts to study and recover the wreckage were hampered by financial and transportation challenges. In 2010, the ship was still submerged, its metal hull severely corroded from decades of exposure to seawater. Analysis confirmed that the ship was in a state of advanced disrepair. Without conservation measures, it would decay beyond repair.