High Quality Content by WIKIPEDIA articles! HMS Juno was a 26-gun Spartan-class sixth-rate frigate of the Royal Navy launched in 1844 at Pembroke. As HMS Juno, she carried out the historic role in 1857 of annexing the Cocos (Keeling) Islands to the British Empire. She was renamed HMS Mariner in January 1878 and then HMS Atalanta two weeks later.