During the Middle Ages, the island was populated by monastic communities. By the 16th century, however, the island was uninhabited and used by pirates as a refuge and base. In 1565, Helier de Carteret, Seigneur of St. Ouen in Jersey, received letters patent from Queen Elizabeth I granting him Sark as a fief in perpetuity on condition that he kept the island free of pirates and occupied by at least forty men who were of her English subjects or swore allegiance to the Crown. This he duly did, leasing 40 parcels of land (known as "Tenements") at a low rent to forty families, mostly from St. Ouen, on condition that a house was built and maintained on each parcel and that "the Tenant" provided one man, armed with a musket, for the defence of the island. The 40 tenements survive to this day, albeit with minor boundary changes. A subsequent attempt by the families to endow a constitution under a bailiff, as in Jersey, was stopped by the Guernsey authorities who resented any attempt to wrest Sark from their bailiwick. In 1844, desperate for funds to continue the operation of the silver mine on the island, the incumbent Seigneur, Ernest le Pelley, obtained Crown permission to mortgage Sark's fief to local privateer John Allaire. After the company running the mine went bankrupt, le Pelley was unable to keep up the mortgage payments and, in 1849, his son Pierre Carey le Pelley, the new Seigneur, was forced to sell the fief to Marie Collings for a total of £1,383 (£6,000 less the sum borrowed and an accumulated interest of £616.13s). During World War II, the island, along with the other Channel Islands, was occupied by German forces between 1940 and 1945. German military rule on Sark began on 4 July 1940, the day after the Guernsey "Kommandant" Major Albrecht Lanz and his interpreter and chief of staff Major Maas visited the island to inform the Dame and Seigneur (Sibyl and Robert Hathaway) of the new regime. British Commandos raided the island several times. Operation Basalt, during the night of 3–4 October 1942, captured a prisoner, and Hardtack 7 was a failed British landing in December 1943. Sark was finally liberated on 10 May 1945, a full day after Guernsey. In August 1990, an unemployed French nuclear physicist named André Gardes, armed with a semi-automatic weapon, attempted an invasion of Sark.