The S-class submarines of the Royal Navy were originally designed and built during the modernisation of the submarine force in the early 1930s to meet the need for smaller boats to patrol the restricted waters of the North Sea and the Mediterranean Sea, replacing the British H-class submarines. As part of the major naval construction for the Royal Navy during the Second World War, the S class became the single largest group of submarines ever built for the Royal Navy. A total of 62 were constructed over a period of 15 years, with fifty of the "improved" S class being launched between 1940 and 1945. Service The submarines operated in the waters around the United Kingdom and in the Mediterranean, and later in the Far East after being fitted with extra tankage. After the war S-class boats continued to serve in the Royal Navy until the 1960s. The last operational boat in the Royal Navy was , launched in 1945 and scrapped in February 1966. was in Israeli service as INS Tanin and was decommissioned in 1972. Several S-class submarines were sold on or lent to other navies: Netherlands 1 Portugal 3 France 4 Israel 2. (HMS Springer as INS Tanin (S71), landed commandos and fought with an Egyptian ship in the Six-Day War) A modified version was ordered by the Turkish navy in 1939 as the . Service losses Of the twelve S-class boats that were in service in 1939, only three survived to see the end of World War II, a loss rate that inspired the song "Twelve Little S-Boats", based on a nursery rhyme originally written by Septimus Winner in 1868. Twelve little S-boats "go to it" like Bevin, Starfish goes a bit too far — then there were eleven. Eleven watchful S-boats doing fine and then Seahorse fails to answer — so there are ten. Ten stocky S-boats in a ragged line, Sterlet drops and stops out — leaving us nine. Nine plucky S-boats, all pursuing Fate, Shark is overtaken — now we are eight. Eight sturdy S-boats, men from Hants and Devon, Salmon now is overdue — and so the number's seven. Seven gallant S-boats, trying all their tricks, Spearfish tries a newer one — down we come to six. Six tireless S-boats fighting to survive, No reply from Swordfish — so we tally five. Five scrubby S-boats, patrolling close inshore, Snapper takes a short