HMY Kethailes was a steam yacht that was launched in 1903 as a private pleasure craft and commissioned into the Royal Navy in 1914.

On 24 September 1914 Johnston voluntarily handed over the yacht (later receiving financial compensation) to the Admiralty, for use as an Armed Naval Auxiliary.

[3] On 28 September 1917 Kethailes was first-on-scene and assisted the cargo ship William Middleton, which had hit a mine laid by SM UC-75.

[4] The Commanding Officer, Lt Comdr Lane RNR and his crew were commended for preventing William Middleton from sinking.

[10] In July 2022 CWGC accepted identification research of Able Seaman Frederick Dyer, previously buried as an unknown sailor in a communal grave in the Churchyard of St Matthew Borth, Dyfed.