|Class Name :
|Unit Run :
|D'Kyr plus 8 others built in total. 3 have been lost in all. 8 have been retired from service.
- DestroyedSeleya - Destroyed Tal'Kyr 
2144 - 2154, remained in service until 2204
||Length : 600 m 
Beam : 286 m 
Height : 222 m 
Decks : 11
1,970,000 metric tons
6 x Phase cannon, total output 3,250 TeraWatts
4 x C Class photon torpedo tube with 90 rounds
|Defence Systems :
||Standard shield system, total capacity 283,500 TeraJoules
Standard Monotanium Single hull.
Low level Structural Integrity Field
(TOS scale) :
|Normal Cruise : 6
Maximum Cruise : 6.5
Maximum Rated : 7 for 5 hours.
|Strength Indices :
(Galaxy class = 1,000)
|Beam Firepower : 65
Torpedo Firepower : 9
Weapon Range and Accuracy : 50
Shield Strength : 105
Hull Armour : 1.25
Speed : 179
Combat Manoeuvrability : 1,530
|Overall Strength Index :
|Diplomatic Capability :
|Expected Hull Life :
|Refit Cycle :
||Minor : 1 year
Standard : 1 years
Major : 8 years
The D'Kyr class was a Vulcans vessel in use during the mid 22nd century. It bore the distinctive Vulcan design philosophy of that era - a ring nacelle with axial hull. For the D'Kyr, however, the hull does not penetrate through the centre of the ring nacelle but splits into two support struts.  Notable ships included the Tal'Kyr, which was attacked and badly damaged by the Tholians in 2152  and the Seleya. The Seleya was sent to chart the thermobaric barrier surrounding the Delphic Expanse in late 2152; it became caught in the clouds and pulled into the Expanse. The Vankaara was sent to locate the Seleya and was in turn lost. The fate of the Seleya remained a mystery until 2153, when the NX-01 Enterprise discovered the ship adrift in an asteroid field in the Expanse. The crew had attempted to line the ship's hull with Trellium-D to protect it from the spatial anomalies to be found in the expanse, unaware of the damaging effect this substance had on the Vulcan brain. As a result the whole crew was subject to permanent brain damage inducing paranoia and violent impulses.  D'Kyr class ships formed part of the Vulcan fleet which attempted to invade Andorian space in 2154 ; later in the year the ships were used as aprt of the fleet which tracked down the Romulan drone ship which had been terrorising various species around Romulan space in an attempt to provoke a war. 
The D'Kyr is a much larger vessel than the Surak class ship, approaching 600 metres in length. This is far too large for any ship of this era - the D'Kyr is almost as big as the Galaxy class of two centuries later, and certainly far larger than Kirk's Enterprise.
We do not have a class name on these ships, so as usual I have gone with the name of the first example seen as the class name until something better comes along.
As with most Vulcan ships of this era, the most interesting feature is the nacelle. Once again the D'kyr employs a ring nacelle, but this time the hull splits and goes around the sides of the ring rather than through the axis. What advantage this might convey is open to question, though some have suggested an interesting possibility - during combat the nacelle ring may be able to rotate by 90 degrees so that it is parallel to the hull. This would mean that the nacelle was hidden behind the main hull, which would give it considerable extra protection (at least so long as the ships followed the usual Trek practice of staying in the same plane with one another all the time). This theory is supported by "Future Tense" where the disabled Tal'Kyr's nacelle ring was partially rotated, which could mean that the crew was setting up for combat when the ship was attacked. However, we see D'Kyr class ships in combat a couple of times during the Vulcan civil war arc in season 4 of Enterprise, and at no point do any of them fold their ring down flat. In a battle with Enterprise a D'Kyr even takes damage to her ring - if folding it flat was a tactic which could be used in combat, you would have certainly have expected it to be used here.
There are some other interesting possibilities for a moveable ring - folding it down would make the hull quite flat and streamlined, which would be handy if you wanted to design the ship to be able to land on a planet. It might also be some kind of variable geometry to aid in agility at warp speed, something which would be even more effective if the ring could turn side to side, as it looks like it might. The idea of a moveable ring is not certain, though - it may be that the rings are indeed fixed and the Tal'Kyr's ring was simply blasted partially loose during the battle.
Although I'm not completely sure, the D'Kyr looks like a heavily modified re-use of the Tarellian ship first seen in TNGs "Haven" and used many times since as various alien ships.