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Understanding What Happened
to Sub Marine Explorer

Since 2004, Sub Marine Explorer has been the subject of detailed analysis and documentation, including LIDAR scanning, corrosion studies, biological assessment of the marine organisms growing on and in it, and a detailed archaeological and historical analysis. 

A detailed side-scan sonar and magnetometer survey of the cove where Sub Marine Explorer lies was conducted as well as an AUV (autonomous underwater vehicle) multi-beam sonar survey of portions of the offshore zone surrounding Isla San Telmo, and several dives to the pearl beds where Sub Marine Explorer likely worked in August 1869. 

An assessment of the colonization of Sub Marine Explorer by marine organisms by Dr. Erich Horgan of Woods Hole Oceanographic Institute found a diverse range of organisms common to both the nearby tidal rocks, as well some from deeper water that have adapted to the darker, enclosed environment inside the submarine. Finally, the ongoing assessment of Explorer in 2008 included a detailed work to complete interpretive reconstruction drawings in the field and an evaluation of ongoing mechanical damage to the submarine. For the first time, a comprehensive sense of how the submarine was built, how it operated, and the incredible level of sophistication inherent in Julius  Kroehl’s forgotten craft was apparent. 

A very significant aspect of the 2008 field season was the survey of the surrounding seabed–the submerged maritime cultural landscape in which Explorer worked–by a REMUS autonomous underwater vehicle (AUV). 

That survey, conducted by Woods Hole Oceanographic Institute’s Mike Purcell and Greg Packard, found that the waters immediately in front of the cove where Explorer lies were shallow and most likely were not where the submarine had operated, despite the proximity to the cove, because none of the depths were close to those recorded in the contemporary news accounts of Sub Marine Explorer’s dives. The waters to the west, however, were deeper, and it appears that dive operations would have taken Sub Marine Explorer offshore. Dives on the pearl beds in the area found very few oysters in depths greater than 24 meters, suggesting that Explorer’s technological benefit took it into waters with less than optimal conditions for the oysters and pearls it sought. In doing so, the dives also exposed Explorer’s crew to decompression sickness. This was a breakthrough observation, and a critical aspect in assessing Explorer’s failure in a larger context. 

Assessing the landscape also shows that the placement of the wreck is therefore not an accident, even if it eventually drifted or was pulled ashore. An aerial perspective of the submarine shows that it lies in the cove, hemmed by submerged rocks and reefs that make its drifting into the cove highly improbable. More than likely, the craft lies in close proximity to the site where it was laid up and ultimately abandoned. Sub Marine Explorer is part of the landscape encompassed by the cove, the inshore area, site of the secondary activities associated with the oyster harvesting, and in a broader context the island of San Telmo and its surrounding waters, whose submerged oyster beds were the site of Sub Marine Explorer’s dives and hence the source of the pearls and shells collected by its crew. The only known contemporary account of the submersible’s operations places it at Isla San Telmo in late 1869, and at the conclusion of its last known dives, “it was decided, the experiment having proved a complete success, to lay the machine up in an adjacent cove” (New York Times, August 19, 1869). 

The cove was the probable base of operations for the submarine, as it lies in the lee of the island and away from the open ocean, and as such would have housed a temporary camp for the pearling operation. While the most recent charts of San Telmo date to the mid-20th century and were insufficient to determine whether the immediate offshore area was of sufficient depth to the be the site of Explorer’s 1869 dives, which reportedly reached a depth of 30 m (100 ft), the sonar survey of the waters surrounding Isla San Telmo in 2008 determined that the area offshore and to the west were shallower, although some areas had depths approaching 24 meters. Assessment of the area, which included dives with local pearl divers from the neighboring village of La Esmerelda, as well as biological assessment dives by scuba conducted by Dr. Horgan, revealed rock-based clusters populated by larger numbers of immature (smaller) oysters, in the shallows along the western (windward) side of San Telmo.    

The channel between San Telmo and neighboring Isla del Rey, while possessing an ideal habitat for oysters (a channel lined with rocks), also revealed oysters that are more immature, clustered in waters that do not exceed 10 meters in depth at high tide. While based at Isla San Telmo, and in the once-rich pearling waters of the archipelago, Explorer was not in an ideal location. The depths it is reported to have worked required a tow of the submarine away from the island, into open ocean waters on the windward side, where its dives were at depths beyond the ideal range for the oysters it sought.

The pearl oyster, Pinctada mazatlanica, thrives on hard rocky bottoms in shallow depths up to 21 meters, but does not live in water exceeding 33 meters in depth (Galtsoff 1950:14 and Mackenzie 1999:58).   

Sub Marine Explorer arrived too late, and its technological advantage of a large craft capable of sustained operations at depth was for naught as it was forced to look for oysters in deeper waters that had not been fished out. Operating at depth for several hours, Sub Marine Explorer surfaced, quickly equalized to surface pressure, and its crew then opened the hatches. Under these circumstances, as we reconstructed the dive profiles, safe diving limits were exceeded, exposing the crew to decompression sickness (the bends). This explained references to illness among the crew in 1869. Combined with a less than optimal return on pearls and the illness of the crew, as well as a likely failure to continue to raise funds for the Pacific Pearl Company after three years of no returns for investors, the probable reasons for the abandonment of the submarine on an isolated Pacific island are now much clearer. 

The final results of the various field seasons have been provided to the Panamánian government along with a series of recommendations for the ongoing preservation of the submarine. The rate of corrosion is such that recovery and conservation of the craft may be prohibitively expensive and possibly not successful in the long term. Other options have been suggested, and even if no further work is undertaken, the technology and characteristics of a rare, surviving example of Civil War-era nautical technology have been preserved through the detailed plans prepared as part of this project.