Shamrock I is launched on June 24, 1899 and christened by Lady Russell of Killowen. Its build has been shrouded by secrecy and its hull is hidden by canvas, as was the case for Thistle, in 1887. The 1895 challenger Valkyrie III is refitted to be sailed as a trial horse for Shamrock I. Soon after its launch, Shamrock I races against the Prince of Wales' yacht, Britannia. The Irish challenger outpaces the royal yacht in two regattas on the Solent. Shamrock I arrives in New York on August 18, 1899, and sails daily to train the crew for the Cup races. During the second cup race, on the first windward leg, Shamrock's topmast snaps and the challenger withdraws. The same evening a new spar is fitted. The Irishmen add four tonnes of ballast, so the yacht is re-measured on October 18, but its sailing performance is not improved. The Irish yacht's Steel mast is too bendy. During the 1899 yachting season, the boat goes through six sets of sails. "On November 2, 1899, Shamrock I leaves New York and is towed back to Great Britain by Lipton's steam yacht, Erin, via the Azores. It is dry-docked on arrival. [In] 1901 Shamrock I is refitted by Lipton and sails as a trial horse for his new challenger, Shamrock II, a George L. Watson design. [In April] 1903, Shamrock I is refitted again and sails as a trial horse for Shamrock III. On May 28, 1903, with 41 crewmen onboard, Shamrock I sails to New York and races against Shamrock III before the Cup. After the Cup, Lipton tries to sell his two yachts, without success. [In] 1914 Shamrock I sails against Shamrock IV off Cowes before Lipton's fourth challenger sails across the Atlantic.