A silver cargo worth some $18 million has been found in a sunken ship at the bottom of the North Atlantic Ocean, a marine salvage and shipwreck exploration company said Monday.

Shares of Florida-based Odyssey Marine Exploration Inc. rose 6.46 percent after it announced finding the wreck of the SS Mantola, which was torpedoed by a German submarine on Feb. 9, 1917, during the World War I.

In 1917, the British Ministry of War Transport paid a War Risk Insurance Claim for £110,000 (in 1917 value) for silver that was on board the Mantola when she sank. This sum would equate to more than 600,000 ounces of silver based on silver prices in 1917.

At a price of $30 per troy ounce, 600,000 ounces of silver would be worth about $18 million.

Last month the British government awarded Odyssey a salvage contract for the cargo whereby the U.S. company will retain 80 percent of the net silver value recovered from the wreck, which lies in 2,500 feet of water.

Odyssey used a remotely-operated marine vehicle to find and inspect the Mantola, which is about 100 miles from another wreck the company is salvaging, the SS Gairsoppa, believed to have been carrying as much as seven million ounces of silver.

The incremental costs to search for the Mantola were low, as this was a contingency project in the event that our team successfully completed the SS Gairsoppa search early, said Mark Gordon, president of Odyssey.

We are planning to conduct the recovery expedition in conjunction with the Gairsoppa recovery, which will also make the operation very cost efficient. Securing our ownership rights prior to recovery and funding our business from cash-flow produced from operations has been a key focus for us. Our share of this successful recovery in 2012 will contribute significantly to our operational funding.

Salvage operations on both the Gairsoppa and the Mantola are expected to begin next spring.