An explosive problem: How the navy cleans up WW II underwater leftovers

Lt. Zach Johnson tumbles backwards off a grey inflatable boat, splashing into the blue water of Conception Bay South. He's headed to the bottom of the ocean to clean up a problem that's been there for 76 years.

The calm water, filled with sailboats and Zodiacs, was a very different scene in 1942.

German U-boats lurked under the surface, targeting ships moving iron ore from the mines on Bell Island.

Four ships were sunk, taking with them more than 60 sailors andabout 50 rounds of explosives.

Even decades later, those undetonated explosivesstill pose a risk.

• Armed Forces to sweep explosives from Nazi-sunk ships off Newfoundland

"In this case we're lucky we know what they are," said Johnson, a navy lieutenant with the fleet diving unit in Halifax.

"We're able to go back into the publications and look how they work. So basically our divers are briefed on what the risks with these particular pieces of ammunition are and how they work how they function and so, you know, don't hit it in this particular place where we know it's gonna set it off."

These shells were never fired so they should still be in the safe mode, but Johnson said you never know after decades of degradation.

There are plenty of precautions to keep everyone safe.

You get down there and realize the ammunition locker was blown apart in 1941.- Lt. Zach Johnson

Boats are being kept away while divers work below the surface to find the munitions.

But there are always surprises.

For the SS Saganaga, the shells were stored in the munitions locker, but that's not where they are decades later.

"You get down there and realize the ammunition locker was blown apart in 1942, the ammunition strewn all over this rotting deck, and you have to dig through old pieces of metal to do it," said Johnson

It's physically demanding work for the divers.

These shells are heavy

"You can't just stand up and pick it up, you have to swim these things around. At the same time you have to be very gentle with them, you can't slam them down, and so it can be a fairly challenging dive."

Once retrieved, the shells are loaded into a net and hoisted up to the surface. Sea water keeps them safe, but when they dry out they can explode.

So they're wrapped in blankets and doused with water to keep them wet until they can be safely disposed.

For these important pieces of Second World War history, the Cambrai Rifle Range in Makinsons is where it ends.

They're loaded into a pit with some explosives and then blown up.

Then the team goes to find some more.

The navy diversknow they won't get them all.

"There are some that end up, just due to the nature of the degradation, possibly buried 10 feet under five collapse decks that we can't get to," said Johnson.

But when the crew is done, the shipwrecks will be safe for recreational divers a reminder of a very different time in Conception Bay.

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