As war in Europe loomed in 1938, the Anderson shelter was designed to offer UK householders rudimentary protection during air raids.
By the outbreak of World War II in September 1939, Anderson shelters had been installed in the gardens of around 1.5 million houses in the areas most expected to be targeted by the Luftwaffe. A further 2.1 million were installed over the course of the war.
Of those 3.6 million shelters, just a handful remain in place today. This site contains information about the 15 I know of, together with information about the history, design and construction of the Anderson shelter.