KWAJALEIN ATOLL, –
This joint team, led by Naval Sea Systems Command’s Office of the Supervisor of Salvage and Diving (SUPSALV) and sponsored by the U.S. Army Space and Missile Defense Command /Army Forces Strategic Command (USASMDC/ ARSTRAT), spent two years researching, planning and preparing for this unprecedented undertaking: removing oil from up to 173 tanks of a heavy cruiser warship.
With its pristine diving conditions, inverted orientation and shallow depth profile, this wreck is uniquely situated to make such an operation feasible. Experience and technology leveraged from other sunken vessel oil removal projects conducted by SUPSALV (ex-USS CHEHALIS in 2010 and USS MISSESSINEWA in 2003) prepared the team for the challenging mission. With support from the Military Sea Lift Command (MSC) vessel USNS SALVOR (one of the Navy’s Safeguard-class salvage ships) and the deployed Mobile Diving and Salvage Unit, Company 1-8 from Pearl Harbor, HI, the team conducted over 100 hot taps through the hull of the ship to recover 228, 900 gallons of oil. The mission took place from August through October 2018, during which the joint team removed all of the accessible oil entrapped in the sunken vessel’s 173 fuel tanks. The main objective of this exercise was to eliminate the potential for a catastrophic release of the oil from the deteriorating wreck and protect the surrounding marine environment and population from potential contamination.
The ex-USS PRINZ EUGEN was commissioned as heavy cruiser in the German Navy in 1940 and later allotted to the U.S. Navy in 1946 as a war prize. The ship was then assigned as a test ship for use in the Able and Baker Atomic Tests in Bikini Atoll. Following the second test, she had sustained minor damage that could not be repaired due to the radioactivity. She was taken to Kwajalein Atoll awaiting further instructions. As she slowly took on water, an attempt was made to tow her out of the Atoll, but she capsized and sank while in transit. She now lies completely inverted offshore Enubuj Island. As the hull has aged, there had been increasing signs of oil leakage over the years.
USASMDC/ARSTRAT, who operates the Ronald Reagan Ballistic Missile Test Facility on the island of Kwajalein, just 3.6 miles from the wreck site, is highly committed to stewarding the marine resources of the Atoll. By advocating to remove potentially polluting oil from the ex-USS PRINZ EUGEN, they sought to protect both the health and safety of the local people and the environment of the Marshall Islands while also ensuring continued safe and uninterrupted operations of the range.
Beginning in 2016, in preparation for this undertaking, SUPSALV engineers conducted extensive research by gathering ship’s drawings, examining documents associated with the last known loading of the vessel and ultimately building a 3-D digital hull model of the sunken vessel to aide in planning. Subsequently in 2017, SUPSALV divers conducted a survey of PRINZ EUGEN which included drilling and sampling 14 of the 173 fuel oil tanks. The team confirmed that oil remained aboard, collected a sample for chemical analysis, and tested the hull integrity to ensure the remaining metal plate would safely support current oil removal techniques (“hot tapping”). Based on the results of this survey, an official exercise to remove all accessible oil from the wreck was authorized and planned commenced to conduct the operation during the ideal weather window in late summer 2018.
Months before the oil removal operation began, SUPSALV’s Emergency Ship Salvage Material (ESSM) oil spill response team worked tirelessly to select, assemble and deploy the right combination of equipment, tools and consumables to support the planned 45-day operation in the remote, austere location of Kwajalein. The load-out included “hot tap” oil extraction systems, submersible pumping systems, oil spill response resources, tank close-out and patching supplies, and other innovative diver tools. An extensive market search was also conducted to identify and charter a commercial oil tanker to collect the recovered petroleum product and ultimately transport it for disposal or recycling at the conclusion of the operation. The oil tanker vessel HUMBER, owned and operated by Global Energy out of Singapore, was selected and hired by the SUPSALV team for the job. The US Army Garrison - Kwajalein Atoll provided the extensive on-site logistics support, including provisioning the two support ships and lifting and handling of the mission equipment, to enable the mobilization of this large-scale operation. Their flexibility during planning and execution of this operation in a challenging environment where resources are limited was commendable.
The tanker vessel HUMBER and USNS SALVOR arrived in Kwajalein on 28 August 2018 and the next week was spent loading provisions and equipment and laying the anchor legs for both vessels to moor at the wreck site. SUPSALV staged the emergency oil spill response equipment onshore Kwajalein, including boom tow boats, inflatable oil containment boom and oil skimmers in the event of a significant release during operations. Thousands of feet of sorbent boom were also staged on both vessels moored over the wreck for immediate, smaller scale responses.
The two ships supporting the operation needed to be positioned directly above PRINZ EUGEN in order to effectively conduct oil removal operations. This task was made more challenging by the close proximity of the wreck to the neighboring shoreline which would not allow the ships to drop the shoreward anchors due to the shallow depth. Therefore, SUPSALV arranged for use of the U.S. Army Garrison – Kwajalein Atoll’s harbor Tug MYSTIC to collect the anchors at the pier and drop them in place. This process was completed on 4 September when the ships successfully finalized their 4-point moor over PRINZ ENGEN.
The Fuel Tanks
There are 143 external fuel tanks aboard PRINZ EUGEN and 30 internal fuel tanks potentially containing oil. Upon arrival, the divers installed an intricate navigation grid system developed by the SUPSALV engineers onto the hull of the wreck in order to visually show the divers where the tank boundaries were from outside the hull. The grid was based on the ship’s structural drawings (frames and bulkheads) which defined each fuel tank. By measuring a specific distance from the grid lines, divers were able to locate the highest point in each external fuel tank and drill a small test hole to determine if oil was present. Of the 143 external tanks, 80 were found to contain oil and hot tapping procedures were employed to drill into the tank using a closed system to safely pump out the contents.
Hot Tapping and Pumping
After identifying that a tank contained oil, a large 3-foot by 3-foot area on the high point of the tank was cleared of marine growth and hot tapping equipment was installed. This included securing a flange to the hull with self-drilling, self-tapping fasteners, attaching a ball valve to the flange, and finally placing the tapper assembly (hole saw) on top, driven by an underwater hydraulic drill. Once the penetration was made with the hole saw through the hull, the valve was closed and the cutter assembly removed in order to attach the suction hose and pumping assembly. Once the pump was secure and all valves and hose connections were checked, the pump began transferring the oil from the wreck to the tanker vessel Humber. This phase began on 6 September and ran through 13 October.
Once all 80 external tanks containing oil were addressed, the team proceeded to investigate the 30 internal tanks. These tanks are located behind the external tanks deeper into the ship and required an innovative hot tap extension tool to drill through the external tank hole and extend to the inner tank wall to drill with a slightly smaller hole saw. The first internal hot tap using this new extension tool was successfully completed on 1 October, marking a noteworthy advancement in technology. Once the inner tank was penetrated, the contents of the internal tank were allowed to bleed into the external tank in order to be pumped off. This process usually happened rapidly due to the nature of oil wanting to float to the highest point of any tank. During the tapping and pumping phase, 159 of the total 173 tanks were tested and 92 of them were found to contain recoverable oil and each one was successfully hot tapped. 14 tanks were determined to be inaccessible, meaning the internal or external structure of the wreck prevented the team from being able to hot tap via conventional means or using the new hot tap extension tool. These tanks require more invasive measures by cutting away or otherwise removing the structure to access them to even test for oil. This approach will significantly change the appearance of the wreck in these 14 locations and would have required time beyond what the weather window and ships’ schedules permitted during this mission. It is unknown if these inaccessible tanks still contain oil, however, they are protected deeper in the ship and pose little to no risk of a sudden, significant release.
Clean-up and Demobilization
The team commenced the cleanup after each tank was hot tapped and pumped free of recoverable oil, by sealing it with a permanent, tamper-proof dome assembly to prevent any subsequent leakage of residual oil clingage left in the tank. This also ensured that the wreck, a popular dive site, is safe for continued recreational diving. Though the remaining oil clingage poses no risk of sudden catastrophic release or harm to the environment, small droplets may slowly escape through the ships piping systems or other outlets as the wreck's structure continues to corrode with age.
During demobilization, the MDSU divers cleared the wreck of all hot tap equipment, hoses, and tools while the SUPSALV team derigged the equipment from the ships’ decks. A sweep of the neighboring Enubuj (Carlson) beach adjacent to the PRINZ EUGEN wreck was also conducted to ensure no trash or debris was left behind. The final week of the operation included getting the tanker HUMBER back underway to Singapore with her load of oil for disposal, removing the mooring legs from the wreck site, and repackaging all equipment for return shipment to the U.S. The USNS SALVOR also departed for her next assignment.
Kwajalein Atoll is now safe from the risk of an oil spill from PRINZ EUGEN. The success of this operation was due to the excellent cooperation, coordination, and the flexibility to adapt and overcome immense political and logistical challenges by all parties involved. The Supervisor of Salvage & Diving, CAPT Keith Lehnhardt, commended the joint team for successfully completing such a historic mission stating, “This project was an incredible opportunity to showcase the U.S. Navy Salvage community’s capabilities and serves as an example of exceptional partnership for future oil spill responses, salvage operations, and other emergencies.”