A dozen more Revolutionary War-era cannons have been found and raised from the Savannah River

A crew guides a cannon lifted from the Savannah River in mid-January.

(CNN)Archaeologists have hauled up 12 more Revolutionary War-era cannons from the Savannah River, a remarkable find that raises questions about which vessels carried them and precisely how they ended up in the water.

The local district of the US Army Corps of Engineers, which is in charge of the deepening of the channel in Savannah's busy harbor, on Tuesday posted a video and photos about the discoveries.
Last month's raising of the rusted artifacts brings to 15 the number of cannons, plus fragments of another, found in the past year during preparation for the port expansion project.
      "There is no telling what all is down there," Corps district archaeologist Andrea Farmer told CNN, saying "so much of the river is unknown."
        That's because the river bottom is strewn with everything from Native American pottery that was pushed downstream, to a small amount of debris from a Civil War ironclad that sank in 1864 and other vessels lost over time in the colonial Georgia city. Archaeologists said they would have expected the cannons to have been found during maintenance dredging.
          One of the artillery pieces is kept in a protective trough at a Savannah facility.
          When the first three cannons were located during dredging last February east of the town's famous River Street, near Old Fort Jackson, archaeologists and Britain's Royal Navy offered an intriguing possibility about their source.
          They said -- based on measurements and appearance -- the cannons may be from the HMS Rose, a famed British warship that mixed it up with colonists during the revolution or, as the UK calls it, the War of Independence. Nearly 250 years ago, the British scuttled the ship in the Savannah River to block the channel and prevent French ships from coming to the aid of colonists trying to retake the city.
          But they quickly learned that theory does not hold water, so to speak. The HMS Rose, it turns out, was sunk farther up river and its artillery apparently was removed beforehand.
          British archives indicate the cannons may have belonged to two or more British troop transports also sunk to block the channel.
          Farmer says officials believe the cannons are associated with the Revolutionary War. Experts are looking for any distinguishing marks or features that can help verify their provenance, such as a known inventory of what a ship was carrying. The goal is to match the artifacts with a specific vessel or wreck.

          So why were British troops in Savannah?

          A short refresher course might be in order to answer that question.
          The 13 colonies, determined to gain their independence, fought the forces of King George III on land and sea. The British, hoping they would gain support from royalists in the South, took Savannah in 1778, only to find themselves defending it less than a year later.
          The HMS Rose, with its 20 cannons and 160 sailors, and other vessels were brought in to help fellow Redcoats.
          The British warships Phoenix and Rose engage with American vessels in New York during the Revolutionary War. Experts say the Rose led to the formation of the precursor of the US Navy.
          The warship was already famous, having been a "scourge" on the colonists, as the Royal Navy puts it. It quelled smuggling in Rhode Island, prompting the formation of the forerunner of the US Navy. The Rose fought in and patrolled New York waterways and parts of the Eastern Seaboard before it sojourned south.
          In Savannah, the vessel was sacrificed by the Royal Navy on September 19, 1779, to keep French allies from joining the American siege at that point in the river.
          "The French had blockaded the port of Savannah, getting ready to attack," Stephen James, an archaeologist with Commonwealth Heritage Group, says in the Corps video. "They scuttled these troop transports to keep the French out and basically saved the city early on from being taken over. They plugged the channel to where ... the French could not come up and take the city."
          Two cannons are displayed during an Army Corps of Engineers briefing in early 2021.
          It's possible that the cannons may have belonged to the HMS Venus or HMS Savannah, which were burned or scuttled as part of the British strategy.
          The British eventually won the battle and controlled Savannah until almost war's end.
          The cannons appear to date to the mid-1700s -- predating the Civil War by about a century -- which aligns closely with the HMS Rose's history. The ones found last February are about 5 feet long.
          Further study and the removal of sediment on the cannons may provide information on when and where they were manufactured.
          "I think it's fantastic and interesting when artifacts from maritime history come to light," Cmdr. Jim Morley, serving as the UK's assistant naval attache in Washington, told CNN last year. "It just gives us an opportunity to look back at our common maritime history and history in general."
          CNN reached out Tuesday to Morley for further comment.

          More research and analysis lies ahead

          The Army Corps of Engineers utilizes contractors for much of its work, and that is the case with historic artifacts found in the water, such as the cannons found in a deep spot called Five Fathom Hole.
          Salvage divers assisted Commonwealth Heritage Group in lifting of the ordnance from the channel. Divers can work only during high or low tide and when no freighters are passing directly overhead. Conditions are hazardous and the government has discouraged treasure hunters from diving in these waters.
          A diver enters the water in December 2021. Crews have explored Revolutionary War and Civil War sites.