Bremen cog, Medieval merchant vessel at German Maritime Museum in Bremerhaven, Germany.

The Bremen cog is the wreck of a merchant ship dated to about 1380, displayed at the German Maritime Museum in Bremerhaven. Its open oak hull, built with a carvel bottom and clinker sides, measures 24 m long, 8 m in the beam and just over 4 m high at the sides. Almost the complete starboard side and a third of the port side were reassembled; masts, decks and rigging are gone.

Dredging in the Weser near Rablinghausen on 8 October 1962 exposed the wreck, which dendrochronology of its oak timbers dated to about 1380. The incomplete hull suggests the cog drifted from its shipyard before completion. After recovery, parts were stored in water tanks, and from 1972 reassembled in the Koggehalle under constant spraying. Conservation in a polyethylene glycol tank ended in May 2000.

The cog's name comes from the Hanseatic trading network that used such vessels across the North and Baltic Seas. Three near-identical replicas exist: Ubena von Bremen, Hansekogge and Roland von Bremen. The Ubena, launched in 1990, sails from Bremerhaven's Neuer Hafen and covers about 1,200 nautical miles under sail each year.

The hull stands open in the Koggehalle of the German Maritime Museum in Bremerhaven, held upright by a frame of grey metal poles, with no decks, masts or stairs to climb. Visitors walk around it on a tiled floor and can look straight into the shell; the timber is displayed under constant sprinkling and controlled conditions, so keep to the marked path.

The hull was found incomplete, and tools from the shipyard were still inside it, which is why researchers think a storm flood swept it away from its building site before it was finished. In 2022, artefacts found near the Teerhof in Bremen suggested the cog was built there.