Hydra () was an ironclad warship of the Greek Navy, named for Hydra, one of the Saronic Gulf islands which played a key role in the war at sea during the Greek War of Independence. The lead ship of her class of ironclads, she was ordered in 1885 in response to a crisis in the Balkans and Ottoman naval expansion. The ship was launched in 1889 and delivered to Greece by 1892. She was armed with a main battery of three guns and five guns, and had a top speed of .