History of Orkney should continue to be observed in Orkney and Shetland. Thus the udal succession and mode of land tenure (that is, absolute freehold as distinguished from feudal tenure) lingered to some extent, and the remaining udallers held their lands and passed them on without written title. The islands cluster round the huge deep-water anchorage of Scapa Flow like a protecting hand, and in both World War I and World War II, the Royal Navy had a major base there, enabling them to challenge any attempt by German warships to emerge into the ocean through the Norwegian Sea. After the Armistice in
Naval warfare of World War I of mines, occasionally attempting to lure the British fleet into battle (one of such attempts was the bombardment of Yarmouth and Lowestoft) in the hopes of weakening them enough to break the blockade or allow the High Seas Fleet to attack British shipping and trade. Britain strove to maintain the blockade and, if possible, to damage the German fleet enough to remove the threat to the islands and free the Grand Fleet for use elsewhere. In 1918 the U.S. Navy with British help laid the North Sea Mine Barrage designed to keep u-boats from slipping into the Atlantic. Major battles