Richard
The TARTAR he served on would have been the torpedo-boat destroyer (TBD) launched in 1907 and handed over to the Navy the following year: quite a full history may be found on Wiki:
https://en.wikipedia.org/wiki/HMS_Tartar_(1907)
In 1904 the new First Sea Lord, Admiral ‘Jacky’ Fisher, ordered that all future torpedo-boat destroyers should be oil-fired and over the next few years a group of twelve ships were ordered from different shipbuilders, to their own designs using oil-fired steam turbines.
The ships were given names previously used by small ships of the Royal Navy, and because these included names such as Zulu, Mohawk and Maori, they became known as the Tribal class.
Although the ships did achieve very high speeds, 34 – 36 knots, compared to 24 – 26 knots of the coal-fired ships, the ships were not deemed a great success: none of them were good ‘sea boats’ (i.e. they rolled too much and shipped too much water) and it was found that fuel consumption was higher than predicted.
TARTAR when completed was part of the First Destroyer Flotilla attached to the Blenheim, based at Chatham. An outline of her service during the time your relative was serving onboard:
1908 – 16 April commissioned at Southampton; then to the Medway to join the 1st DF. Exercises locally and North Sea; port calls: Harwich / Kirkwall / Portsmouth
1909 – exercises locally and port calls: Harwich / South Queensferry / Fortrose / Lowestoft / Portsmouth
1910 – as before: exercises in North Sea and port calls: Harwich / Lowestoft / Portsmouth / Portland
1911 – as before: exercises locally and North Sea: port calls: Harwich / Portsmouth / Kirkwall
Small vessels like these early TBD’s (the term was later abbreviated to Destroyer) were not big enough to carry their own admin staff, so they had what was known as a “parent ship”, that looked after the pay and secretarial work. This would usually be the vessels that were known as Depot Ships, at this time usually an elderly warship retired from active work. The Blenheim was converted for this role in 1907. I would imagine he was drafted to Blenheim and then allocated to one of the TBD’s she was “parenting”. It became the usual practice later to note the name of any destroyer a man was allocated to from the Depot Ship, on the Service Record, usually in brackets after the Depot Ships name, such as Blenheim (Tartar). This clearly did not happen with this record – probably because it was not yet a widespread practice.
TARTAR photo:
https://www.worldnavalships.com/ship_photo.php?ProdID=111502