Important was the help of Hydra in the national liberation struggle in 1821. The Eve of Holy Struggle, find the island full strength, economic and military. The island had a population of about 28,000 residents, has 186 battleships ships with 2,400 guns and tonnage of 45,000 tons, manned by crews 5,400 men. Fair Ibrahim called Hydra "Little England".

Hydra, Spetses with and Psara, played a decisive role in the Revolution of 1821 from the commercial and naval fleets in the service of the race. Hydra as Admiral Miaoulis, Anthony Economou, Tombazis, Sachtouris, Voulgaris, the Kriezis Tsamados, Sahin, the Vokoi Brothers, the congressman Matrozos and Pepin, and many others, promoted to leading figures in the Revolution.

The revolution in Hydra officially declared on April 16, 1821 by Anthony Economou and people who overcame the reservations of notables. The Hydraiki fleet with a fleet of Spetses and Psara dominated the sea during the seven year war, thus contributing to the liberation of Greece, sacrificing many lives, ships and money and bringing leaders and activists.

Intense but it was the reaction of strong effort in Hydra I. Kapodistrias abolish the privileges enjoyed the island by then.

After liberation begins a long period of decline and recession on the island for about a century, Hydra despite its small size and deepening economic decline, given the politics of the country a President of the Republic, five prime ministers, many ministers.

George Koundoriotis was Chairman of the Executive during the Revolution, member of the Council on Kapodistrias Othona Prime Minister and Minister of the Navy.

Anthony Kriezis, Dimitrios Voulgaris, seven times Prime Minister, Athanasios Miaoulis, three times Prime Minister and Petros Voulgaris, Prime Minister of Greece.