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"You were willing to betray your captain to save your people; I sacrificed my body and mind to protect mine. I have the Human's face, but inside I remain Klingon."
– Voq, to Michael Burnham, after the collapse of his cover as Ash Tyler, 2256 ("The Wolf Inside")


Ash Tyler, Klingon


choH'a' was a form of species reassignment protocol used by the Klingon House of Mo'Kai during the Federation-Klingon War. It was specifically designed to gather intelligence on Starfleet through infiltration. (DIS: "The War Without, The War Within") In short, it involved surgically modifying a Klingon to look like a donor Human, whose DNA, memories and consciousnesses were also harvested and added on top of the Klingon identity, which was nonetheless expected to remain intact and waiting to be reactivated.

The method was not detectable by Starfleet even with a full set of physical scans, which did find masses of scar tissue surrounding the organs, but attributed them to torture. Nor was the Klingon personality detected by the highly effective manchurian test, which aimed to detect what used to be called brainwashing: commands or personality engrams underneath a functioning consciousness. However, more advanced testing, including Chondroblast-cell scans, did reveal a more troubling picture, hinting at procedures like marrow-diminutions or neurological therapy. (DIS: "Despite Yourself")

Ash Tyler's active and latent DNA scans

A medical scan compares Ash Tyler's active Human DNA and anatomy with his latent Klingon DNA and anatomy.

The only confirmed application of the protocol was the transformation of Voq in 2256, for the purposes of infiltrating USS Discovery and learning its secrets. When asked if there were others, a House of Mo'Kai operative involved in the operation claimed that he was the test case. (DIS: "The Wolf Inside", "The War Without, The War Within")

A Human Starfleet officer called Ash Tyler was captured at the Battle of the Binary Stars. His DNA was harvested, his consciousness reconstructed and his memory rebuilt. (DIS: "Vaulting Ambition")

The Klingon subject for the procedure, Voq, was then modified into a "shell" that resembled Tyler. This involved traumatic surgery, including the flaying of his skin and sawing his heart into pieces. His limbs were opened up and his Radius, femurs and even his Spinal cord were shortened. The tips of his fingers were shaved down, his bones cracked open and crushed. As a result of these procedures, scar tissue surrounded all organs. (DIS: "Despite Yourself", "Vaulting Ambition", "The War Without, The War Within")

Finally, Voq's psyche was then grafted into Tyler's. Doctor Hugh Culber theorized that a new personality might have been placed on top of the original one, with the original personality still intact underneath. (DIS: "Despite Yourself", "Vaulting Ambition")

Following the procedure, the new Tyler was successfully inserted on the Discovery as planned. (DIS: "Choose Your Pain", "Lethe") However, even while still believing he was Tyler, memories of the surgery resurfaced. Tyler mistook them for torture and started to exhibit symptoms that were recognized as PTSD. (DIS: "Into the Forest I Go") Later L'Rell attempted to re-active his Klingon personality through a Klingon prayer. This went awry, leaving the Human and Klingon personalities to war and causing mental anguish. Tyler nearly died, until L'Rell purged Voq's mind from Tyler's brain. (DIS: "Despite Yourself", "Vaulting Ambition")

In the Klingon language, choH'a' translates to "change" (choH), with the suffix 'a' indicating a greater intensity than the basic word, so choH'a' means "great change".

Arne Darvin, a Klingon spy encountered a decade later, might be another case of choH'a'. Like Voq, Darvin was altered to look Human, in a way implied to be surgical (in "Trials and Tribble-ations"). However, McCoy was able to ascertain that he was a Klingon due to a simple body scan indicating wrong heartbeat and body temperature, suggesting Darvin's modifications were either less sophisticated, or that Starfleet had mastered detecting this type of infiltration. (Pike's experience in "Brother" demonstrates that at some point during the war Starfleet tightened identify authentication in at least some scenarios) It is also worth noting that "Darvin" did not appear to think he was a Human, which would imply that either the re-activation of the Klingon personality, apparently intended for Voq but failed, had been perfected, or High Chancellor L'Rell, who saw Voq's horrific fate first-hand, had decided to ban the use of personality suppression in choH'a' spies.

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