The Mars warship was carrying hundreds of soldiers when it exploded in the Baltic Sea in 1564 during the Northern Seven Years’ War. 
 
 Cannons, hand grenades, and up to a thousand soldiers were on board the large Swedish warship when it exploded in the Baltic Sea, 454 years ago. 
 
 The ship, known as Mars, belonged to the Swedish navy and was one of Northern Europe’s largest and most feared naval vessels used in the Northern Seven Years’ War. 
 
 The remains were discovered at the bottom of the Baltic Sea in 2011, near to the Swedish island of Öland. 
 
 The latest discoveries from the wreckage were revealed during a press conference in Öland. 
 
 “This year, we have come closer to the people aboard. We found more skeletal parts, including a femur with trauma around the knee which we believe to stem from a sharp-edged weapon,” says maritime archaeologist Rolf Fabricius Warming, who is one of the researchers involved in the investigation. 
 
 “We also found large guns and a hand grenade. We can see from the wreckage that it was a very intense and tough battle. Between 800 and 1,000 men were on board. That is comparable to the population of an entire medium-sized town at the time. Most of them died in the explosion or when the ship sank into the watery depths,” he says. 
 
 Read More: Researchers discover remains of sunken Swedish warship 
 
 The ship contained silver treasure 
 
 Researchers had previously discovered silver treasure among the Mars wreckage. This time, one of the most spectacular finds was a large grapnel (grappling hook) an anchor-like hook, which hung from the bowsprits of warships and was used to cling onto another ships in order to board it. 
 
 Grapnels are illustrated in historical sources from the 16th century, but no actual surviving examples are known apart from this particular one, says Warming. 
 
 “It’s totally unique. Together with other exciting finds, it can shed new light on Medieval and Early Modern naval warfare. ,” he says, and adds that the divers also found remains of possible arms and armour, including helmets and swords. 
 
 Read More: The Viking’s grave and the sunken ship 
 
 Danish and Lübeckian soldiers were on board 
 
 Mars sunk due to a gunpowder explosion at the front of the ship. But shortly before, it had been under attack by Danish and Lübeckian warships according to written sources. 
 
 “Soldiers fought with hand grenades, lances, and spears, which they threw down from the masts. The fighting was structured and carefully calculated but an absolute ruckus” says Warming. 
 
 Danish soldiers, allied with soldiers from Lübeck, managed to defeat the Swedish crew and capture the warship. When the ship exploded and sank, it had three to four hundred Dano-Lübeckian soldiers aboard. 
 
 A 3D- model of the shipwreck. (Video: Ocean Discovery / Ingemar Lundgren) 
 
 A Swedish change of tactics 
 
 The new examination of the Mars shipwreck provides new insights into the events that took place between Denmark and Sweden during the Northern Seven Years’ War between 1563 and 1570. 
 
 They have documented a change in Swedish tactics from a focus on close quarter combat to long distance fighting, as indicated by large cannons up to 4.8 metres long. 
 
 Despite the large cannons, the Swedish crew did not manage to avoid engaging in close quarter combat with their enemies. The soldiers aboard were positioned underneath a net that covered the deck and was designed to prevent the enemy from jumping on board – a so-called anti-boarding net. 
 
 “We know about the use of anti-boarding nets in this battle from richly detailed written sources. The Swedish Admiral, Jacob Bagge, describes in his own account of the battle how he was injured in the shoulder by a javelin thrown from one of the fighting tops of the enemy ships. t. We are told he became furious and began shooting at those who had injured him with arquebuses so that they fell into the net below,” says Warming. 
 
 Read More: Medieval shipwreck hints at psychological warfare 
 
 A snapshot of a moment in time 
 
 Until 2011, historians relied on written sources for information about what happened to Mars, including letters from the Danish admiral Herluf Trolle and the Swedish admiral Jacob Bagge, and official royal documents. 
 
 But the shipwreck provides an entirely different type of documentation. 
 
 “There’s some ‘fake news’ in the written sources. Many people wanted to claim the honour of defeating the Mars for various political reasons. But when we study the wreckage itself we see a large congruency between the wreck site and the historical sources. One of the most striking observations was that it really was sunk by a large explosion. It was so violent that the front of the ship lies 40 metres away from the other remains,” says Warming. 
 
 For maritime archaeologist Mikkel Thomsen from the Viking Ship Museum, Denmark, looking at the well preserved, and complete remains captures a snapshot of a moment in time. 
 
 “You really feel that you’re in the killing fields,” says Thomsen, who was not involved in the study. 
 
 “The wreckage gives a snapshot of a piece of military and political history. It’s also an international history as the Seven Years’ War was fought across national boundaries,” he says. 
 
 Read More: Historic shipwrecks could be preserved in the Antarctic 
 
 Divers filmed the shipwreck 
 
 The Mars remains lay 70 metres beneath the surface of the Baltic Sea—so deep that researchers could not go down themselves to investigate. Instead, professional divers and ROVs were deployed to film the wreck. 
 
 The footage and recordings were used to create 3D-models of the wreck and the artefacts found on the site. 
 
 Scientists and divers have not been granted permission to touch or remove anything from the wreck or nearby, which might be for the best, according to Thomsen. 
 
 “The Baltic Sea has extremely good preservation conditions. The water is low in oxygen, cold, and fresh. So boring worms that are usually the greatest threat to wood cannot live there,” says Thomsen. 
 
 Lifting the remains out of the water would lead to breakdown and damage of the materials, he says. 
 
 “Moreover, it would be very difficult and extremely expensive to retrieve it from such deep water,” says Thomsen. 
 
 The exploration of Mars was carried out by researchers from the Marine Research Institute MARIS at Södertörn University in Sweden, and divers from the diving organization GUE, Västervik Museum, Ocean Discovery, and MMT. 
 
 Fifteen divers and ten researchers have participated in the latest exploration of the ship. 
 
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 Read the original article in Danish at Videnskab.dk ||||| The Baltic Sea is a graveyard of ships that have sunk over the past few centuries, in particular the two World Wars. German maritime expert Thomas Dehling has an eye on shipwrecks and sunken objects - and their exact positions. 
 
 DW: How many shipwrecked boats are there in the Baltic Sea? 
 
 Thomas Dehling: I don't know the figure for the entire Baltic Sea, but in German waters - about 16,000 square kilometers (6000 square miles), less than a tenth of the Baltic Sea - there are quite a lot, roughly 1,000 objects that we know about. 
 
 In the Baltic Sea, we have quite a lot of shipwrecks due to the two World Wars, more than in other seas. Most of the objects are from the early 20th century, but there is one shipwreck in Finnish waters that is more than 400 years old. In our part of the Baltic, there's an old wooden shipwreck that dates to the 15th or 16th century, the archeologists aren't sure. There's not much left but the cargo was still there: copper disks, a really unusual find so far north. 
 
 We regularly survey the objects, especially those that are potentially dangerous to shipping, depending on the importance of the object and the sea lane, maybe once a year or only once every 25 years. 
 
 How unusual would a 
 
 off the Swedish coast be? 
 
 There are several WWII Russian submarine shipwrecks in the Baltic Sea, that isn't unusual. In the case of the shipwreck off the Swedish coast, it depends on how old it is. Because of the wars, there are English submarines in German waters in the North Sea, a Polish shipwreck in the Baltic Sea, a German shipwreck in Polish waters. If the Russian submarine is not that old, it is obvious that a Russian submarine entered Swedish waters clandestinely. 
 
 Is the Baltic Sea popular with recreational divers? 
 
 Yes it is - and it's dangerous. Very often fishing nets get caught in the objects and you have to be very experienced to dive there. That's why we don't disseminate our information on the shipwrecks. 
 
 But there's a map on your website? 
 
 Yes, but you won't find an object when you use that map because it's not that precise. Of course we have to inform the maritime community about obstructions that might hinder their traffic, but we don't inform the public about objects that might be of historic interest - only people who can claim that they need to have the information. 
 
 Have you charted all of the objects in your sector by now, or do you still find new ones? 
 
 In our part of the Baltic Sea, we still find 10 to 15 objects every year that we didn't know about before, thanks to the modern technology on our ships that lets us survey the seafloor in much more detail. And many of the objects aren't large shipwrecks, but much smaller, or partially submerged. And they're not the ones that are potentially dangerous to shipping, we know about those. We don't remove anything, we inform the water and shipping administration, and it's up to them to decide whether to remove an object or set up a buoy. 
 
 Thomas Dehling heads the hydrographic surveying division at Germany's Federal Maritime and Hydrographic Agency (BSH), which provides maritime service for the shipping. The agency is based in Hamburg and Rostock.
– The Baltic Sea's trove of shipwrecks has preserved all kinds of history—much of it about war—and recently sparked fears of a fresh conflict in Europe. Bordered by Scandinavia, Finland, the Baltics, the North European Plain, and accessible by Russia, one sliver of the sea contains about 1,000 known shipwreck objects, maritime expert Thomas Dehling tells Deutsche Welle. He's referring to what slumbers in 6,000-square-miles of "German waters," which he says represent not even a tenth of the full sea. "Many of the objects aren't large shipwrecks, but much smaller, or partially submerged [ones]," he says. "We still find 10 to 15 objects every year that we didn't know about before." Most are from World War I and II, but not all: A Swedish three-masted warship called the Mars went down in 1564 while battling the Danes and may have been cursed by its own cannons, National Geographic reported last year. Discovered in 2011, the warship sank when its cannons overheated and exploded during battle; legend says it was cursed because Swedish kings repurposed church bells to build the cannons. In another Baltic find, 168 bottles of perfectly preserved 19th-century French champagne were discovered on a sunken schooner near Finland, Smithsonian reports. "It was incredible," says a scientist of the bubbly that later sold for up to $100,000 a bottle. Then last year, Sweden saw its Cold War fears revived—and concerns about modern Russia heightened—when said it spotted a foreign sub in its waters. Sweden now says a Russian sub may have indeed been found in the Baltic ... but the wreckage is thought to be that of a WWI vessel that likely went down almost 100 years ago. (Read about a "sickening" shipwreck find in the Arctic.)