The most important moment in the history of the island was its involvement in the Liberation War of 1821. In 1821, Hydra had a strong shipping industry, wealthy ship owners, and crews prepared for war. The Hydra notables had been initiated into the Society of Friends (a secret organization determined to end Turkish domination of Greece) before 1820. But while the people of Spetses raised the flag of revolution on March 26, the Hydra notables initially seemed hesitant (probably because of the disaster from the Orlov Revolt in 1770).
The revolution was finally proclaimed on April 14 with an ecclesiastical procession and a written revolutionary proclamation titled "Passport of Greek Fighting Ships." Hydra captain Andreas Ikonomou (1785 - 1821) played a decisive role in getting Hydra involved in the liberation war of 1821 despite the opposition of the island's leaders. He was assassinated for this reason by followers of A. Liontou in December 1821.
As well as the links mentioned in the articles and generally the key texts of sources about the Saronic Gulf area of Exploring Greece