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Notes : The D-12 is a variation on the standard B'Rel class Bird of Prey, introduced in 2348. The D-12s introduced a new type of cloaking device into the Klingon fleet, intended to provide a much greater degree of stealth from the latest generation of sensors coming into use in the alpha quadrant. However, the class was never satisfactory in service; the cloaking device was far bulkier than any previous model and had a significantly greater power requirement. In order to install it in a hull as small as the D-12's, half the torpedo armament had to be sacrificed together with the entire cargo bay and a third of the crew quarters. Since operating the cloaking device required an extra seven crew members to be carried over the standard maximum B'Rel complement, the D-12 class was highly cramped even by Klingon standards. Despite these shortcomings the D-12's entered service in small numbers throughout the next seven years. In 2357 fifteen of the crew of the KHL Kolnar were killed when a section of the hull blew out as the vessel cloaked; two months later a similar accident killed eleven warriors on the HKL Nak'Leth. Investigations indicated that a design fault in the plasma coils of the cloaking device was causing the system to emit high levels of neutron radiation, resulting in serious neutron fatigue to a large section of the hull of almost every ship.  The D-12 class was retired from service en masse in 2359.

Most were scrapped or used as targets in live fire exercises, but nine ships were sold to private individuals. These have generally been used by mercenaries and pirates, changing hands many times over the years. The most notable use of a D-12 was by the Klingon renegades Lursa and B'Etor of the House of Duras, who used a D-12 during their plot to gain control of a Trilithium weapon in 2371. When the USS Enterprise-D intervened the sisters were able to penetrate the vessels shields and inflict catastrophic damage to the star drive section, resulting in its destruction in a warp core breech. Although the saucer section was able to escape this explosion, it crashed on the planet Veridian III where it was later stripped and abandoned. The D-12, along with the Renegades, was destroyed by the Enterprise during the battle.