Skuldelev 3: a coastal trader possibly used by a farmer.

As Orcadians well know, Scapa Flow was used as a naval base by the British fleet during both World Wars. The location is of strategic importance for control of the North Sea, and it forms a useful natural harbour. Prior to the construction of the Churchill Barriers, access was secured by the use of sunken blockships (which ultimately proved insufficient as a German U-boat was able to penetrate these defences and sink HMS Royal Oak).

Blockships were also used by the Danes almost 900 years earlier. The remains of five ships scuttled for this purpose are on display in the Viking Ship Museum in Roskilde, Denmark. These significant finds have been of great importance to modern understanding of traditional Nordic boat-building techniques.

During the time of the Vikings (approx.750-1100 AD), Roskilde was the largest town in the Danish realm and a key trade hub for shipping. It was the centre of royal and religious power, with a Christian cathedral on the hilltop in the centre of town, overlooking the harbour. This all made it a potential target for attack.

Roskilde sits at the end of a fjord. There were two channels by which enemy ships could reach the town (and a third which was too difficult to navigate without local knowledge). From the time an invading force was sighted at mouth of Roskilde Fjord, the race would be on to alert the townsfolk. In the 11th Century, King Svend Estridsen devised a system of barriers at Skuldelev, 20 km to the North. This would control shipping traffic while allowing time for a series of signal fires (beacons) to send warning. There is no evidence that an invading fleet ever actually attacked.

Chart showing navigation channels near Skuldelev.

The five vessels found at Skuldelev formed part of a defensive system consisting of piles of stones, driven posts, and floating palisades. These ships were filled with stones and scuttled between 1060 and 1070 AD. They may have been old ships scuttled at the end of their seaworthy lives, but represent a unique collection with varying designs and functions:

Skuldelev 1: the merchant ship.

• Skuldelev 1: A 16m long, sturdy, ocean-going trader capable of plying the North Sea and North Atlantic with a crew of 6-8.
• Skuldelev 2: A 30m, oak-built longship built near Dublin, which could carry around 70 warriors, travel at 15 knots, and cross the North Sea in 3 days. 60 oarsmen could keep it moving at speed even with no wind in the sails.
• Skuldelev 3: a 14m small coastal trader of a type which may have belonged to a farmer and had a crew of 5-8.
• Skuldelev 5: A small, 17m warship, which could carry about 30 warriors and was suitable for traversing the Baltic Sea.
• Skuldelev 6: An 11m fishing boat built in Norway, possibly for whaling or seal hunting, but later converted to a transport.
• Skuldelev 4 was once thought to be a separate vessel but is now considered part of the longship.

These ships are on display in a museum which was purpose-built to hold them in 1969, a few years after the ships were raised. Reconstructions are situated at the adjacent boatyard, along with many other vessels in various stages of construction, which are built using traditional methods (and smell strongly of tar).

Between May and September visitors can join a crew and go sailing in the Fjord.

Reconstruction of a longship at the Viking Ship Museum in Roskilde.