Chang's Bird-of-Prey

Chang's Bird-of-Prey was a prototype Klingon Bird-of-Prey commanded by General Chang in his efforts to discourage the potential peace talks between the Federation and the Klingon Empire. The vessel was equipped with a cloaking device that somehow allowed the vessel to fire its torpedoes while cloaked, an ability once considered impossible on other vessels, due to power constraints.

As the USS Enterprise (NCC-1701-A) escorted Kronos One, which was transporting Chancellor Gorkon to Earth for peace negotiations, the cloaked Bird-of-Prey hid directly under the Enterprise. The only sign of its presence was a large amount of neutron radiation, which was detected too late as the Enterprise crew witnessed what appeared to be two torpedoes seemingly fired from their vessel hitting Kronos One. The incident was further complicated by the work of saboteurs who altered Enterprise's databanks to give the appearance that two torpedoes had been fired. As a result, Gorkon was assassinated, and Captain James T. Kirk and Doctor Leonard McCoy- who had transported over to try and treat Gorkon's injuries- were arrested for his murder. Fortunately, the Enterprise daringly managed to rescue them, disobeying orders from Starfleet Command.

Despite some skepticism from his fellow officers, Captain Spock began an investigation of the ship, reasoning that someone involved in the attack had to have been on board the Enterprise in order to reprogram their computer to register the missing torpedoes or to fire the torpedoes in the first place. Having assembled the evidence, he was able to determine the existence of this vessel, as it seemed to be the most logical explanation, if theoretical. His theory was proven true as he gleaned the information by way of mind meld with Lieutenant Valeris, who had been found to be in league with the conspirators, learning that there was only one such ship. After learning the new, secret location for the peace conference from Captain Hikaru Sulu, on the USS Excelsior, both vessels headed to Khitomer where the Bird-of-Prey was waiting for them.

As Chang quoted Shakespeare over all the comm channels, his ship opened fire on the helpless Enterprise, causing it heavy damage. The Excelsior, arriving late, was just as incapable of tracking Chang's ship and was hit as well. Spock determined that despite its cloak, the Bird-of-Prey still released plasma exhaust, and based on an idea from Cmdr. Uhura, installed equipment, with McCoy's help, on a photon torpedo designed to catalog gaseous anomalies. Once fired, the torpedo wound around space, slowly beginning to lock in on the exhaust from the Bird-of-Prey, until it impacted on the unshielded bridge, killing Chang and his command crew and exposing the ship. Combined fire from the Enterprise and Excelsior then destroyed Chang's ship. 

Background
The model explosion of this vessel was later reused for the destruction of the Duras sisters' Bird-of-Prey in.

Apocrypha
In the novelization of the movie, this ship is called the Dakronh. Also in the novelization, Spock further elaborates that the traces of plasma exhaust are detectable because the ship must slightly reduce cloaking power when firing its weapons.

This may be in reference to the Hamlet character King Claudius, who, like Chang, was responsible for the faceless murder of a rightful ruler, although the motivations are different.

The vessel is featured as a playable ship in two missions of Star Trek: Klingon Academy. Named the IKS guHmoH, the ship is used by the player's character to spy on meetings between Melkor and his supporters using a highly-advanced sensor array that requires the player to bring their ship within fifty meters of Melkor's bridge.

A more advanced version of this ship is available in Star Trek Online.

Changs Bird-of-Prey