Mars, also known as Makalös ("peerless; astounding"), traditionally referred to as Jutehataren ("The Jute Hater"), was a Swedish warship that was built between 1561 and 1563. She was the leading ship of King Eric XIV of Sweden's fleet and one of the largest warships of the time. In 1564, during the Northern Seven Years' War, she caught fire and exploded during the First battle of Öland in the Baltic Sea.

Eric XIV of Sweden succeeded Gustav Vasa in 1560. He needed to consolidate the still-disputed independence of Sweden that had been achieved by his father, but was ambitious to build upon that. A strong navy could give Sweden the opportunity to tax foreign ships, so helping the economy. The keel of Mars was laid in 1561 and she was complete by the autumn of 1563, by which time the Northern Seven Years' War had broken out.

Mars was built during a time when both ship construction methods and naval tactics were undergoing change and development. Carvel construction had arrived in northern European waters during the previous century, but this was not a single-step process and techniques were still being developed, as the archaeology of the wreck of Mars shows. The naval tactics of the time were moving from a focus on boarding to greater emphasis on stand-off gunnery to defeat the enemy. Again, this was a slow transition, ultimately producing the line of battle that became standard from c. 1672. At the time that Mars was built, the major maritime power of Europe (the Dutch) favoured close-range melee actions, with individual ships picking an opponent of roughly their own size.

The First battle of Öland took place over two days, starting on the 30th May 1564. The first day went well for the Swedish fleet. They sank one Lübeckian ship and badly damaged the Danish flagship Fortuna. Both sides withdrew for the night to rest after the action, but when they re-engaged in the morning, the Swedish fleet had become dispersed due to bad weather overnight. Without the close support of the rest of the fleet, Mars was attacked by several enemy ships and some incendiaries set her alight. Admiral Jacob Bagge, the Swedish commander, ordered her colours to be struck. Mars was boarded by some 300 Lübeckians – eager to claim their share of the prize, but the fire reached the magazine and she blew up in a massive explosion. Eye-witnesses described the foremast being projected into the air "like a cross-bow bolt". She sank very quickly.

The wreck of Mars settled to the sea bed at a depth of 75 metres (246 ft) 12 nautical miles (22 km; 14 mi) north-east of Öland. At this depth and with the exact location unknown, the highly valuable bronze guns were out of reach of any historic salvage attempt. After the explosion, the ship's hull was broken into three main pieces at the surface and these sank to the bottom independently. With the forward part of the hull mostly destroyed, these major fragments were the port side, the starboard side and the lower part of the hull.

The wreck site was located by the company Ocean Discovery in 2011 after a long-term search with sidescan sonar. It was clear that the wreck of a large wooden vessel had been found, with many cast bronze cannon. The initial archaeological investigation was carried out by a collaboration of the Maritime Archaeological Research Institute (MARIS) at Södertörn University, MMT (a company that carries out marine surveys, mostly for the oil and gas industry), Ocean Discovery (the company that located the site) and the TV production company Deep Sea Productions. The depth required divers to used mixed gas and rebreather techniques. As well as extensive visits by divers, some of the archaeological investigation was carried out by photography from ROVs, with multibeam sonars and a bottom-based acoustic scanning technique (called "Blueview").

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57°08′25″N 17°20′56″E / 57.14028°N 17.34889°E / 57.14028; 17.34889