The D-7 class battle cruiser was first encountered by Humanity when the first Starship Enterprise met one in 2151. The date of service entry is unknown, but by 2151 the Klingons already had significant numbers of these ships in service so a date of no later than 2146 seems to be likely. The D7 was far more powerful and advanced than the NX class Enterprise, and was available to the Klingons in far greater numbers as of the early 2150s.

In layout the D-7 set the standard for all Klingon designs up until the present day. The bulk of the ship's colume is in the large engineering hull attached to the two nacelles, with a small secondary hull mounted on the end of a long 'neck' section that projected forwards. This concentrated the vessels mass towards the rear, making it easier for the engines to change the vessels attitude in space. The weapons of the original D7 comprised two torpedo tubes, one in the head facing directly forwards and one in the engineering hull facing due aft. There may have been other weapons also.

Facilities were also included to support ground troops, though this is not so significant on Klingon vessels as on Human or Federation ones; since virtually all Klingon warriors are well trained and experienced in hand to hand combat, any vessel with a transporter is capable of landing significant ground troops.

A D7 class vessel was used by a group of Klingon fundamentalists to depart for the Delta Quadrant in approximately 2275. Following the dictates of a religious prophecy the ship journied for over a century before encountering the USS Voyager, whereupon it was destroyed by its crew in order to fulfil the prophecy.

The urgent need for as many ships as possible during the Dominion war led to the reactivation of the small number of remaining D7 ships, and some of these vessels took part in the Allied assault into Cardassian space which eventually ended the war.

• D752 IKS Groth