problem. Weapons of war that have been deteriorating for decades.

These are ticking time-bombs.

This threat on the ocean floor is known only to a few experts.

It's a race against time.

But is this a race that we can win?

Here at the Polish port of Gdynia, a team of experts is

getting their research vessel ready for an expedition.

The crew includes hydrographers, biologists, and divers from the Marine

Institute in the nearby port of Gdańsk. They've been working together for years.

They're headed for a site located in the Bay of Gdańsk, about half-an-hour's

sailing time away. In 1999, experts made an alarming discovery there.

The team's leader is Benedykt Hac, a former Polish navy officer. His repeated

warnings about these underwater wrecks have made him unpopular with the authorities.

-Some of them don't like what we're doing here. But it's not our job to please

them, or to make things easy for them. This is like a mission for us.

-Full stop! We're there!

Benedykt Hac has been researching this part of the bay for years.

The site is located just two kilometers off the coast.

The pristine beaches along the Bay of Gdańsk are known as the “Polish Riviera"

-- and they're an important part of the country's tourism industry. More than

two-million Europeans spend their summer holidays here every year.

-This is a great place to take a vacation. Just marvellous.

The beaches are beautiful, and the people are friendly.

Some think it's going to be like this forever -- but sadly, that's not the case.

There's a problem here that only a few people know about, and it's very dangerous.

The ship picks up speed to do a sonar scan of the seabed.

Gradually the sonar images reveal a relic from the past that poses a major threat

to the tourist beaches: the wreck of the German hospital ship “Stuttgart.” The

vessel was nearly 170 meters long.

In the autumn of 1943, the ship was anchored at Gdynia — renamed "Gotenhafen"

by the occupying Germans. The vessel was to take

on wounded soldiers from the Eastern Front.

On the morning of October 9th, 378 bombers of the U-S

8th Army Air Force took off from their bases in Britain.

Their mission was to destroy the strategically vital ports and dockyards

along occupied Poland's Baltic coast. They reached the target area in about 4 hours.

The “Stuttgart” took a number of direct hits. Fire broke out on the ship, and

flames lit up the entire harbor area. The crippled vessel was later towed out into

the bay and sunk, so that it wouldn't block the port area.

Today, the "Stuttgart" is just a footnote in history books.

The site of the wreck was soon forgotten.

But in 1999, Benedykt Hac came across the ship's wreckage while he was

mapping the floor of the bay for the Gdańsk Marine Institute.

He's returned to the site often since then. He and his

researchers continue to monitor the condition of the wreck.

Today, divers are braving the ice-cold water to have a look.

The “Stuttgart” lies just 20 meters below the surface.

It's overgrown with seaweed and shellfish.

There's not much left of the vessel, but the wreckage is spread out over an area

that would cover two football fields. In the 1950s, parts of

the ship were blown up in an operation to salvage scrap steel.

At first glance, the wreck and the area around it don't seem to pose a threat.

The divers will use special equipment to take samples from the seabed.

The first sample that's brought up shows why Benedykt Hac is so concerned.

It contains thick globs of oil. The researchers

call them the “Black Tears of the Sea."

Over the years, Hac and his team have collected over 1,000 seabed samples from

this site. But this is the most dangerous material that they've found so far.

It's a thick, foul-smelling mass that contains a lot more oil than sand.

-Look at all that oil!

-I've never seen anything like it here before!

-And it really stinks!

The researchers will take the mud back to their laboratory for closer inspection.

-We're on the brink of an ecological catastrophe here, and I don't think

we can do anything more to prevent it. This site is completely

contaminated. All forms of life have been eradicated.

Benedykt Hac intends to take another 200 seabed samples so that he can

assess the extent of the pollution in the Bay of Gdańsk.

Is the “Stuttgart” just a tragic one-off case? What about all the other sunken

warships that date back to World War II?

Do they pose a threat to the environment as well?

Less than 20 kilometers away, we find the Westerplatte peninsula on the Bay of

Gdańsk. This is where the first shots of World War II

in Europe were fired -- on September 1, 1939.

At 4:45 AM, the German battleship “Schleswig Holstein”

opened fire on Polish positions.

The war would drag on until 1945 -- on land, and at sea. The Allies and the Axis

Powers had huge navies that battled for supremacy.

Allied merchant shipping was often targeted...

...as Germany's navy and air force tried to cut supply lines.

German U-Boats, known as the “Grey Wolves,” took a huge toll on allied shipping.

In June 1942, they destroyed an average of four vessels a day.

But what was the total number of ships that were sunk during the war? And how

many of them pose an environmental threat today, like the the "Stuttgart" does?

To find out more, we travel to Tampa, on Florida's Gulf Coast.

Every year, U-S Coast Guard officials, scientists, and salvage experts take part

in the “Clean Gulf" conference, to exchange ideas on how to combat oil spills at sea.

Among those at this year's session is American biologist and environmental

analyst Dr. Dagmar Schmidt Etkin. In 2004, Etkin began a study on the number

of potentially dangerous wrecks in the world's oceans.

-I collected data on different wrecks in different places, including a number of

German databases -- which I translated from German into English. And some of

those were based on, you know, which U-boat had sunk which vessels.

For two months, Etkin searched through archives and gathered data from sources

around the world. She also examined sonar images of shipwrecks. Etkin's study

included only vessels that had combustion engines, and a weight

of more than 400 gross register tons -- or 150 tons for tankers.

-So I found 8,500-and-something wrecks worldwide -- and about three-quarters of

those were World War II-related. It was a surprise, you know.

These sunken ships can be found near ports, at the sites of naval battles, and along

trade routes. The number of World War II era wrecks is said to be more than 6,300.

They include Italian freighters in the Red Sea and Japanese battleships in the

Pacific. The majority of all wrecks in the last 100

years of navigation history date back to the war.

Many of the ships that went down were filled with fuel or crude oil. No one

knows how much of that material is still trapped in the wrecks -- but Dr. Etkin came

up with an estimate, based on the number of large ships that had combustion engines.

-If I had no information, I looked at the size of the vessel and the type of vessel:

a tanker or a non-tank vessel, a bulk carrier, or a Victory ship, or something

like that. And I assumed, 'Well, let's say at least ten-percent of the oil may still

be on there, maybe 90 percent, maybe all (of it), we dont know' -- so I have a range

of values. So I estimated, using that methodology, estimated about 2.5- to

25-million tons of oil could potentially be on these wrecks. And that was (a cause

for) concern -- because (it) could potentially leak out, and cause the same

kinds of (damage) we see in other oil spills that occur now.

In March 1989, the tanker Exxon Valdez ran aground off the coast of Alaska, and

spilled more than 37,000 tons of crude oil.

But that's just a fraction of the amount of material that's lying in World War II-

era wrecks. Dr. Etkin says that those sunken ships could contain up to 15 million

tons of oil — about 400 times the amount that was spilled by the Exxon Valdez.

-I presented my results on the numbers, and the reaction was: 'This is too big a

problem, and we can't deal with it.' At least here in the United States, but also

in other parts of the world, it's sort of buried. 'It's too complicated. We're not

going to be able to deal with it. It's too expensive and so there's nothing we can do.

Dr. Etkin's study was published more than a decade ago. Since then, experts

have discussed the shipwreck oil problem at conferences, but have taken little action.

The delay has had serious consequences. Some of the oil has already started to

leak — because the tanks where it was stored are starting to disintegrate.

A number of World War II wrecks lie off the east coast of the United States.

This research vessel is operated by the National Oceanic

and Atmospheric Administration, or NOAA for short.

The team on board this ship is constantly on the lookout for World War

II shipwrecks. Today, they're conducting a search off the coast of North Carolina.

Before Dr. Etkin's study was published, there was little interest in these sunken

ships, except among underwater archaeologists.

But the experts at NOAA soon realized that they needed to learn a lot more

about World War II-era wrecks and their potentially deadly contents.

The researchers investigate every sunken ship that they find. They try to determine

the extent of rust damage, and whether any oil is leaking out. They use precision

laser equipment to measure every millimeter of the wreck.

One of NOAA's main tasks is to protect America's ocean- and coastal resources.

This is NOAA heaquarters in Maryland. Marine researcher Lisa Symons is in

charge of monitoring wrecks located in US waters.

Symons was alarmed by Dr. Etkin's study. She hadn't realized that there were so

many wrecks or that they contained so much fuel.

-Well, there was a lot of concern -- and that was something that we were very

aware of. Because there's been a lot of allegations about the waters of the

US, the waters of Germany, Europe, and Japan being full of ticking time-bombs.

Symons wanted to find out more about that threat. In 2010, the U-S Congress

provided one-million dollars to help NOAA determine

the risk posed by these sunken ships.

-It has taken a lot of very painstaking research effort with the archives (and)

going back to the newspaper records. Sometimes you can find living crew

members who remember being on a vessel, or hearing about what happened to a vessel.

The experts use 21 separate criteria to rank shipwrecks in terms of risk, including

the size of the vessel, and the type and amount of oil that's still on board.

Right now, Symons is studying the wreck of the merchant vessel "Coast Trader."

The ship was torpedoed and sunk by a Japanese submarine off the coast of

Washington state in June 1942. The records indicate

that there still could be 1,000 tons of fuel on board.

Such information is often reliable -- but sometimes the researchers can find

out more by using underwater robots. The team wants to determine where the

torpedo actually struck the ship.

Their investigation reveals that the vessel was heavily

damaged, and probably lost a lot of oil as it sank.

So this wreck now seems less of a danger than was first feared. But other wrecks

could contain more oil than the records indicate. NOAA simply doesn't have the

resources to use robots to study all these sunken ships.

The researchers so far have examined 573 major shipwrecks, and have written

detailed reports on 87 of them. 36 were believed to pose a serious threat if all

their oil leaked out. And five World War II-era wrecks were considered a major

risk that could cause serious environmental damage.

-The target audience though is the United States Coast Guard: 'These are the

wrecks in your area of concern that we did analysis of. This is what our findings

are. These are the wrecks that we recommend that you put into active

monitoring.' And it's up to the US Coast Guard to determine whether or not they

want to do an in-water assessment, and then determine

whether or not they want to remove the fuel.

But the U-S Coast Guard has so far not carried out an investigation of any of the

five wrecks listed by NOAA as extremely dangerous -- so

they obviously haven't gotten around to pumping out the oil.

The Coast Guard seems to be taking a “wait and see”approach. The situation is

the same in some other countries that have to deal with this problem.

But the experts at NOAA are taking an active approach.

The agency operates its own satellite and information center.

Here, analysts evaluate data in real time for the U-S Weather Service.

They also work out long-term climate models.

And they monitor the surface of the oceans around the clock, keeping an eye

out for any oil spills. These experts use radar images to spot potential problems.

The researcher is focused on an area off the eastern tip of Long Island, New York.

The NOAA team also pays close attention to the sites in which possibly dangerous

shipwrecks have been found. This one is not on the list of high-risk sites, but the

analyst spots an unusual pattern. It could be an oil leak.

He marks the dark patch, and measures it. It turns out to be nine kilometers long