The Underground resistance reference article from the English Wikipedia on 24-Apr-2004
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Underground resistance

The underground is sometimes a nickname for a resistance movement: "the underground" is also a common name for World War II resistance movements. By extension, the term was also applied to counter-cultural movement(s) many of which sprang up during the 1960s. In a similar sense, the Underground Railroad was an United States anti-slavery movement which helped slaves escape.