Every year at this time, the deep-diving submarine crews of the Hawaii Undersea Research Lab at the University of Hawaii are required to make a few test dives off Oahu in their Pisces submarines. For more than a decade, they’ve multitasked the test dives with searches for notable shipwrecks.

Last month, the HURL team discovered three wrecks off Oahu’s South Shore — two of which turned out to be craft haunted by terrible Navy disasters.

The three craft are S-class submarine USS S-4; Great White Fleet gunboat USS Bennington, PG-4; and a World War II landing craft, USS Chittenden County, LST-561.

"There are a lot of targets we’ve spotted by sonar that we’d like to get to one day," said HURL submarine pilot Terry Kerby, whose 2002 discovery of the Japanese "midget" submarine sunk by the USS Ward off Pearl Harbor capped a decadelong search. "But there isn’t enough time, so we look when we can."

Prior to this year’s search, HURL scientist Steve Price pored over sidescan sonar images identifying potential targets. One fuzzy image he dubbed the "S-boat target" turned out to be exactly that.

"He sure called that one," said Kerby.

THE S-CLASS was the standard U.S. Navy submarine during the years between the wars, and several actually served during World War II. More than 200 feet long, it was the first submarine actually designed by Navy engineers.

In December 1927, off the Massachusetts coast, S-4 was rammed by a Coast Guard destroyer and sank. Despite heavy seas, rescue efforts began immediately.

Although S-4 was not very deep — about 100 feet — the Navy lacked rescue equipment. The last message tapped out by the oxygen-starved crew was, "Is … there … any … hope?"

Four months later, S-4 was raised from the sea floor, the bodies recovered and the submarine repaired. Several divers were awarded the Navy Cross for their heroic, but futile, efforts to rescue the trapped submariners. Forty men died.

Unsuitable for combat operations, S-4 was converted into a test craft for submarine rescue training. A kind of fixed diving bell was attached to the aft deck for egress practice.

S-4 made the rounds of various Navy submarine bases before winding up at Pearl Harbor. Worn out, and considered a hard-luck vessel, S-4 was scuttled south of Barbers Point on May 15, 1936, not to be seen again until this week.

The USS Bennington also suffered one of the Navy’s worst peacetime disasters. Arriving in San Diego on the morning of July 21, 1905, after a stormy passage from Honolulu, the ship was immediately ordered back out to sea to help tow another Navy ship into port. Bennington’s crew were in the midst of recoaling the ship’s fuel bunkers and stoking the furnaces to build up steam when one of the boilers exploded.

The explosion blew out the side of the ship and filled the passageways with scalding steam. More than 60 crewmen were killed and dozens more injured, more than half of the ship’s complement.

Only quick work by a nearby tugboat prevented Bennington from sinking, and heroic actions by the surviving crew resulted in 11 Medals of Honor being awarded by Congress. A monument commemorating the loss stands in San Diego.

The ship, a "protected gunboat" built in 1891 and a participant in the Philippines campaign of the Spanish-American War, was too badly damaged to be seriously considered for a return to service. She was sold for scrap in 1910 and acquired by Matson, which gutted the gunboat and used it for a water and molasses carrier in Hawaii until she was scuttled in 1924.

S-4 and Bennington are fairly intact. The third vessel, tank landing ship USS Chittenden County, was blown apart as a submarine practice target off of Diamond Head on Oct. 21, 1958. The broken hull is scattered in a debris field. Launched in 1944, the LST participated in World War II and the Korean War.

S-4 LIES 3,100 feet deep a little more than 9 miles south of Barbers Point. Bennington and Chittenden County are 3.5 miles south of Diamond Head at depths ranging up to 950 meters (3,000 feet).

"Chittenden County and Bennington are only about 950 meters apart, so we were able to look at both together," said Price. "We made a beeline straight from one to the other."

"Even so, we didn’t have time to look at Bennington’s bow," said Kerby. "Just one pass and a turnaround. The protocol is that one submarine searches while the other stands nearby in case there’s danger."

One unexpected danger was a large rocky outcropping near the ship’s hull that had snagged an enormous fishing or cargo net and held it streaming in the brisk undersea current. Kerby also came across S-4’s broken rudder lying on the sea floor and quickly had to back away as he realized the Pisces was getting too close to the S-4’s looming stern.

Although there are a number of scuttled S-boats in Hawaii waters, Price identified this one as S-4 thanks to an escape-training structure attached to the rear deck.

"Even though the submarine’s sail has been removed, the tower is so unique that we know it’s S-4," said Price. Kerby was amazed that brass gearing in the escape structure still looked brand-new.

The wooden decks of S-4 and Bennington have begun to rot away, and lacy coral and starfish have staked claims to the sites. The round "deck lights" on Bennington, a kind of waterproof skylight, still look into the ship’s interior, and the platforms that once held guns are clearly visible. The scientists were surprised that the LST was sunk with her guns intact.

Looking over Kerby and Price’s shoulders at video of the newly discovered shipwrecks, maritime historian Hans Van Tilburg of the National Oceanic and Atmospheric Administration said, referring to the Hawaii Undersea Research Lab, "Once again, HURL comes through! These are artifacts with significant maritime heritage. The history of the S-4 and the Bennington goes beyond their military service — they helped shape naval and rescue technology to this day."

"It’s part of our history, and matters," said Price. "There are human stories involved. Heroes came out of these disasters."

"Yeah, they’re not just rotting wreckage on the ocean floor," said Kerby.

The HURL crew also revisited the Japanese midget submarine and discovered that the rear hull has begun to break off, and that the "net-cutter" on the bow has been smashed and torn away, ripping holes in the hull.

"Something pretty big must have hit it," said Kerby.

The HURL team left Friday for underwater survey work in the Northwestern Hawaiian Islands.