D5 class

The D5-class battlecruiser was a type of starship introduced by the Klingon Empire in the 2120s that served for over a century and a half. Some of the first Klingon ships fitted with cloaking devices were D5 battlecruisers serving in the 23rd century. 

They shared some design traits with the cruiser used in the same era by the Klingons.

22nd century
These ships were a flexible design as they could be converted into tankers which could carry precious resources such as Deuterium. They also made use of multi-spectral sensors and were composed of diffused bonded monocrystal. 

These ships appeared to have been in common use by the Klingon Defense Force at the time and were much more advanced than the United Earth Starfleet NX class vessels though the Human ships were capable of surviving battle for a short amount of time. 

They were armed with two large disruptor cannons located at the bottom of the central section of the main hull. These weapons were mounted on a type of turret platform which allowed the weapon to rotate and fire at enemy targets regardless of direction. 

23rd century
The D5-class served into the 23rd century, building on the existing mainstay of the Klingon fleet, the D4, and incorporating the first operational versions of newer technologies (e.g., dilithium power focusing). The experience gained with the D5s allowed these technologies to be integrated even better into later designs such as the D6 and D7.