From junked trucks to World War II submarines, vast fields of far-flung wreckage litter the sands beneath the blue-green ocean off Hawaii.
“It’s like an obstacle course under water, especially at Pearl Harbor,” said John Smith, science program director at the Hawaii Undersea Research Laboratory. “Finding the more interesting artefacts is a real challenge.”
A World War II-era Japanese submarine scuttled by the U.S. Navy is the laboratory’s latest significant find among thousands of wrecks, most from the past two centuries.
The ship is one of two I-400 Sensuikan Toku class subs captured in the Pacific a week after Japan surrendered in 1945. Both subs were deliberately sunk by the military when Russian scientists demanded access to them. The 400-foot-long hulks were the largest built before the nuclear ballistic missile subs of the 1960s.
In 2002, the waters off Oahu also yielded a Japanese midget submarine that was hit an hour before Japan’s aerial attack on Pearl Harbor in 1941.
“These are incredibly valuable archaeological sites,” said John Wiltshire, acting director of the Hawaii Undersea Research Laboratory.
“Sometimes in the marine environment, you can preserve things you can’t preserve on land.”
The value of Hawaii’s undersea wreckage is historical rather than monetary. Hawaii’s shipping boom began in the 1800s, well after piracy’s heyday in the late 1600s to mid-1700s.
Most cargo ships navigating the island chain in the 19th century carried goods that would have disintegrated by now, such as sugar, lumber, phosphates, sandalwood and furs, said Rick Rogers, who has written several books on Hawaii’s shipwrecks.
Treasure hunters scouring the Hawaiian ocean bottom for doubloons or pieces of eight are more likely to find submarines, old whaling and merchant ships, fishing boats or 20th-century recreational craft and land vehicles.
Mr. Rogers, a former Army salvage diver, said just one of the few tales of undersea treasure in Hawaii is worth seeking. He has spent 25 years and thousands of dollars searching for two galleons carrying Spain’s entire annual cargo of Oriental trade goods, including porcelain, silk and spices.
References to castaways and shipwrecks in Hawaiian legends stoked Mr. Rogers’ interest in the ships. He said he believes one went down off Maui in the late 16th century, the other in 1693 off the Big Island’s Kona coast.
Finding information on wreck locations takes some work. There are no comprehensive databases or maps of sunken objects, just partial lists, and the Navy limits the release of some locations to prevent looting.
Certain sunken vessels, such as the battleship USS Arizona at Pearl Harbor, are federally protected gravesites and cannot be used for recreational diving. Diving companies, however, have marked the 10 most well known wrecks on Oahu with small buoys.
Having so many military vessels underwater could raise concerns about unexploded munitions, but experts say the material is far from the shoreline and popular beaches.
“I’ve never heard of an instance when anyone has been injured by these old munitions,” said Suzette Farnum, who owns Captain Bruce’s diving company on Oahu’s Waianae coast with her husband. “I’d assume the salt water has kind of trashed them, anyway, but you don’t want to take that chance by picking them up.”
Undersea artifacts in shallower waters actually can benefit the environment, serving as sturdy skeletons for thriving undersea habitats.
The Mahi, a scuttled Navy minesweeper off the Waianae coast, has grown into a 190-foot artificial reef that is home to coral, leaf scorpion fish, puffer fish, trigger fish, eels and magnificent eagle rays. The 100-foot landing craft utility (LCU) ship nearby houses two timid white-tipped reef sharks that flee when divers approach.