During the recently completed 2022 iteration of the biennial Rim of the Pacific Exercise, forces participating in the exercise sank two decommissioned Navy ships as part of what the military calls sink exercises, or SINKEX.

The Navy has conducted these sorts of exercises for decades to give sailors the opportunity to use their weapons on real targets — something the Navy doesn’t have the opportunity to do as often as other branches.

Before they’re towed out to sea, the decommissioned vessels must be defueled and scrubbed of potential toxic chemicals in a series of procedures laid out by the Environmental Protection Agency. But when it comes to tracking the exercises and their environmental impact in Hawaii, the Navy has little data.

The service was unable to provide an exact figure when asked how many ships it has sunk in and around the Hawaiian Islands. In an emailed response, a Navy spokesperson said that “since the early 2000’s, the Navy has conducted an average of two SINKEX’s in the Hawaiian Islands Range Complex each even-numbered year, when RIMPAC exercises are held.”

The training has long been opposed by some environmental groups. In 2011 the Sierra Club and other groups filed a lawsuit against the EPA alleging that it failed to prevent the SINKEX program from exposing the ocean to toxic chemicals, specifically polychlorinated biphenyls, or PCBs — a group of chemicals that are known to be carcinogenic. The plaintiff groups dropped their complaint in 2013 due to a lack of funding, but their criticism of the training has not subsided.

“We don’t support using our ocean as a dumping ground for the Navy’s unwanted vessels,” said Wayne Tanaka, director of the Sierra Club’s Hawaii Chapter. “We’re not confident that they’re able to clean these ships entirely from contaminants, including PCBs. … It also seems to be a very wasteful use of resources that could be put to much better purposes.”

But military professionals insist the training is critical for knowing how both ships and weapons systems work.

“It may seem superfluous, but it is deadly important to all of us that we we know from detect right through to engage how the whole system works,” said Canadian Royal Navy Rear Adm. Christopher Robinson, an officer who served as deputy commander of Combined Task Force RIMPAC during this year’s iteration of the war game. “If you go back to the Second World War … in Hawaii the torpedoes that were being used didn’t function the way people believed them to function.”

Lately, tensions have been simmering in the Pacific once again. Several of the participants in RIMPAC 2022 have been embroiled in territorial disputes with the Chinese navy in the South China Sea, a critical waterway through which more than a third of all global trade travels. China currently has the world’s largest navy — and it is rapidly modernizing its forces and building more ships in a historic buildup.

Chinese forces also recently encircled Taiwan in exercises held in response to a controversial visit by U.S. House Speaker Nancy Pelosi. U.S. Indo-Pacific Commander Adm. John Aquilino, the top officer in the region, told Congress in 2021 before his confirmation to the post that he thought the prospect of a Chinese invasion of Tawian is “much closer to us than most think.”

Warships, being inherently designed to withstand hostile fire from opposing ships, are actually difficult to sink. Vice Adm. Michael Boyle, who oversaw RIMPAC and is commander of the Navy’s San Diego-based 3rd Fleet, said SINKEXes are critical to sailors’ understanding how their weapons actually would be used in the event of a real combat operation to take on an opponent.

“A lot of our weaponry is theoretical; you kind of think you know how it’s going to work,” said Boyle. “To see the effects of the weapon when it hits the ship, does it perform as you expect it was? Does it hit the ship where you thought it would hit? Does it create the damage that you thought it would do?”

This year multinational teams struck and sank the former amphibious transport dock USS Denver and the former guided-missile frigate USS Rodney M. Davis as they pounded them with missiles and other weapons, documented in detail in videos released by the military on social media. There were several firsts, including the use of Air Force MQ-9 Reaper drones.

“A U.S. Air Force platform integrated into a joint and combined force with the video feed shared in an unclassified network (in) real time with the participants, which allowed the chief of the Malaysian navy to watch his missile from his ship hit (the Denver) in real time, which was really significant,” said Boyle. “You watch movies and you assume that this happens all the time, but it doesn’t happen and it’s hard to do. … So that was a first.”

The cleaning process to prepare a ship for a SINKEX is time-consuming. It’s also expensive.

“It’s more expensive to sink a ship than it is to scrap a ship,” said Boyle. “Because to get it to the level of cleanliness, so that we can put it on the ocean floor and allow it to just become a reef, is different than if we were to scrap it.”

But Tanaka said previous examples of ships being sunk to turn into reefs raise doubts. In particular, he points to the sinking of the former aircraft carrier USS Oriskany off the coast of Florida. Decommissioned in 1976, the Oriskany was sold for scrap in 1995 but was repossessed in 1997 when nothing was being done with it.

In 2006 the Navy sank it as part of an artificial reef. The so-called great carrier reef has been controversial. While the Navy spent $20 million on cleaning the Oriskany prior to the sinking, even in complying with EPA guidelines, it an left an estimated 700 pounds of PCBs on the ship, mainly in wiring and bulkhead insulation.

A 2011 study conducted partly by Florida’s Fish and Wildlife Conservation Commission found elevated levels of PCBs were found in fish living within the Oriskany reef. However, despite those results, other ecologists consider the Oriskany to be a healthy reef with large populations of sea life calling it home more than a decade later.

The Navy imposed a 2010 moratorium on the SINKEX training while it conducted a review of the program weighing its benefits, costs and environmental impacts. The training resumed in 2012. Three decommissioned vessels were sunk off Kauai during RIMPAC 2012.

In Hawaii sinking exercises are required to be conducted at least 50 nautical miles from shore and in waters at a depth of at least 6,000 feet. Tanaka said that at that depth it’s not possible for those vessels to become reefs.

“These ships are being sunk in waters way too deep for photosynthetic corals, (but) there are actually extremely rare forms of life found in these deep water habitats that can take centuries to develop,” said Tanaka. “So that’s another concern is what kind of impact these ships are having … in these ecosystems from not just the direct landing of these hulls on the seafloor, but also leaking contaminants (and) corrosion of other materials into the environment.”

When asked whether the Navy has been monitoring the vessels sunk around Hawaii and their potential impacts, a Navy spokesperson said in an email that the depths the ships sink to “precludes them from long-term monitoring.” But Navy officials insist there is no reason for concern or any need to monitor the ships after they sink.

“In 2014 the EPA reviewed the Marine Protection, Research, and Sanctuaries Act General Permit for the Navy’s Sink Exercise (SINKEX) Program and determined (it) does not pose an unreasonable risk of injury to human health or the environment,” a Navy spokesperson said in an email. “Long-term monitoring of SINKEX hulls is not required as they are selected from a list of Navy-approved vessels that have been cleaned in accordance with (EPA) guidelines.”