LÉ Deirdre (P20) was a ship in the Irish Naval Service. She was named after Deirdre, a tragic heroine from Irish mythology who committed suicide after her lover's murder. Deirdre was built as a replacement for the Ton-class minesweepers. She was to have longer range and be a more seaworthy ship for work in the Atlantic. Deirdre became the prototype for the later Emers.] Notably, Deirdre was one of the vessels involved in the 1979 Fastnet race rescue operations, assisting the crews of two yachts - the SV Regardless of Cork and the SV Silver Apple of Howth.