There is a small confusion built into the names, and it has never been tidied up. When the timbers first came out of the fjord, the excavators counted six ships and numbered them accordingly. It emerged later that the wreckage catalogued as Skuldelev 2 and the wreckage catalogued as Skuldelev 4 were two ends of the same hull. Rather than renumber everything and confuse decades of published literature, the museum simply deleted number four and left the rest alone. So the five Skuldelev ships are 1, 2, 3, 5 and 6, and there is no Skuldelev 4, and every guide in Roskilde has been explaining this ever since.

Three of the five were built to carry things rather than fight. Skuldelev 1 is a sturdy ocean-going cargo vessel, possibly of the knarr type: 15.84 metres long, 4.8 in the beam, drawing a metre, built in Sognefjorden in western Norway around 1030 from thick pine planks and repaired again and again over its life with oak and lime in the Oslo Fjord and eastern Denmark. With 90 square metres of sail and only two to four oars, a crew of six to eight could take it into the Baltic, the North Sea and the North Atlantic, at up to 13 knots when conditions allowed. Sixty per cent of it survives. Skuldelev 3, an oak coaster possibly of the byrding type, is smaller and far better preserved — 14 metres by 3.3, carrying four or five tonnes, built somewhere in Denmark around 1040, worked by five to eight people under 45 square metres of sail. Seventy-five per cent of it remains, the most of any of them.

Skuldelev 2 is the ship that changes the story. It is an oak warship, a longship probably of the skeid type, roughly 30 metres long and only 3.8 in the beam, drawing about a metre with a maximum crew of 70 to 80 — a hull shaped for nothing but speed, driven by an estimated 112 square metres of sail and a rowing crew of sixty or more. Dendrochronology dated its timber to the Dublin area around 1042. The Danes who scuttled it were sinking an Irish-built ship from a Norse town on the other side of the North Sea, which says something about how far the traffic ran. It is one of the longest Viking ships ever found and also the most damaged: only about a quarter of it came up. Beside it, Skuldelev 5 shows the other end of the warfleet. Seventeen metres by 2.5, drawing only 0.6, crewed by around thirty, built in the Roskilde area around 1030 from a mixture of oak, pine, ash and alder, with holes cut through the top strake for shield straps. Half of it survives.

Skuldelev 6 refuses to fit the pattern. It measures 11.2 metres by 2.5 and carried both oars and a sail, and its purpose has been argued over since it was raised. It was built in Sognefjorden around 1030, mostly from pine, like Skuldelev 1 — the two may have come from the same tradition, if not the same shore. A crew of five to fifteen could work it, and the likeliest reading is that it started life as a fishing boat. It did not stay one. At some point the hull was rebuilt, probably for coastal cargo, making it what the Norse called a ferje, a catch-all term for a small freight carrier. About seventy per cent of it has survived — a working boat that changed jobs partway through its life.

All five are exhibited at the Viking Ship Museum in Roskilde, which has now reconstructed every one of them, and others have been rebuilt by groups elsewhere in the world. The first replica of Skuldelev 5 came from outside the museum entirely: Sebbe Als, built in 1969 at Augustenborg, which makes 5 knots on oars alone and 12 under sail. The most ambitious was the reconstruction of Skuldelev 2 as Havhingsten fra Glendalough, a €1.34 million project running from August 2000 to September 2004 and consuming almost 40,000 hours of labour; in 2007 she sailed from Roskilde to Dublin and in 2008 she sailed home. Together the five ships are on the Danish Culture Canon, and they have done something few archaeological finds manage — they went back in the water.