More than 200 years after being sunk by Adm. Horatio Nelson and the British fleet, a Danish warship has been discovered on the seabed of Copenhagen Harbor by marine archaeologists. Working in thick sediment and almost zero visibility 15 meters (49 feet) beneath the waves, divers are in a race against time to unearth the 19th-century wreck of the Dannebroge before it becomes a construction site in a new housing district being built off the Danish coast. Denmark’s Viking Ship Museum, which is leading the monthslong underwater excavations, announced its findings on Thursday, 225 years to the day since the...