Katrina Cornwell Vice Admiral Katrina " Kat " Cornwell was a Human female Starfleet flag officer who lived during the mid - 23rd century . She was a psychiatrist or psychologist by training , and had experience treating PTSD . ( ) History . Cornwell was an old acquaintance of Gabriel Lorca , with the two of them being on a first - name basis . ( ) In November of 2256 , she informed Lorca - who had by then been replaced by an impostor from a parallel universe and made captain of the - about a concurrent Klingon attack on Corvan II and ordered him to protect that planetoid . ( ) In December of 2256 , she attended a strategy briefing with Lorca , Terral , and three other admirals . She ordered Lorca to restrict use of the spore drive , since the Klingons might have learned of it and might target the " Discovery " . ( ) A week later , she visited the " Discovery " after Lorca launched an unauthorized rescue mission for Ambassador Sarek , whose ship had been disabled on the way to a diplomatic mission by an explosion that had deliberately been caused by an aide who had turned out to be a logic extremist . Cornwell and Lorca attempted to rekindle their romantic relationship . However , Cornwell made the decision to declare Lorca unfit for command after she tenderly awoke him the morning after , and he responded with a phaser in one hand and his other at her throat ( due to lingering trauma relating to Lorca having recently served time in a Klingon prison ; she was quite upset he kept a phaser under his pillow ) . However , Sarek was too injured to attend his diplomatic mission to Cancri IV , a meeting with a supposed dissenting Klingon faction which could end the war , so Cornwell took Sarek ' s place , planning to recommend Lorca be stripped of command afterwards . The mission turned out to be a trap orchestrated by Klingon General , and Cornwell was captured by Dennas and Ujilli . ( ) Sometime later , Cornwell was kept prisoner by Kol aboard the " Sarcophagus " . Despite weeks of torture , she refused to give up any information . L ' Rell offered her services to Kol as an interrogator in exchange for a cloaking device , but this was a ruse in order to get close to Cornwell . The imprisoned admiral met L ' Rell when the latter arrived in her cell . At her insistence , Cornwell screamed , which She used to distract a guard away from the area . The admiral also learned that L ' Rell wanted to defect to the Federation in exchange for helping her escape , the Klingon having grown disillusioned with how easy her people fell in line with Kol . However , during the escape , L ' Rell and Cornwell were confronted by Kol . Realizing they were unlikely to escape , Cornwell grabbed L ' Rell ' s blade and attacked her , in order to maintain the illusion in front of Kol ' s men . Afterward , L ' Rell hid the unconscious Cornwell in a side room – a room which , to L ' Rell ' s horror , was filled with corpses . ( ) When and Michael Burnham infiltrated the " Sarcophagus " to place sensors on the ship to allow " Discovery " to detect the Klingon ship while it was cloaked , the pair picked up Cornwell ' s life signs and found her in the side room where she had been placed earlier . Discovering L ' Rell present in the same room , Tyler began experiencing intense flashbacks , and was unable to continue the mission . Burnham went on to complete the placement of the sensor on the bridge , while Cornwell tried to bring Tyler back to reality . After Burnham successfully completed the placement of the sensors , Cornwell was beamed back to the " Discovery " along with Tyler , Burnham , and L ' Rell . Cornwell was sent by emergency medical shuttle to Starbase 88 where she underwent surgery . She was expected to make a total recovery . ( ) Following the " Discovery " s return from the mirror universe without Captain Lorca , Cornwell was visibly angered upon hearing of his betrayal , and upset at the presumed death of his prime universe counterpart . She assumed temporary command of the " Discovery " and took it to Starbase 1 , only to discover that the starbase had been overrun and occupied by Klingon forces . When the mirror universe version of proposed that the Federation strike the Klingon homeworld of Qo ' noS directly , by detonating a bomb inside its mantle and rendering it uninhabitable , Cornwell supported the plan , even going so far as to help Georgiou masquerade as her deceased counterpart . However , the " Discovery " s crew objected to the genocide they were about to be complicit in and threatened mutiny . When Specialist Burnham pointed out that Cornwell was making the same mistake she herself had made just before the Battle of the Binary Stars - forgoing Starfleet principles for the sake of survival - Cornwell abandoned the plan . Instead she authorised Burnham to give L ' Rell the bomb ' s detonator so that L ' Rell could use it as leverage to take charge of the Klingon Empire and end hostilities . Cornwell later honored the crew of the " Discovery " for their actions during the war . ( ) Appendices . Background information . Cornwell was portrayed by actress Jayne Brook . The first name " Katrina " was initially only mentioned in the Netflix German voice dubbing list for , but was first spoken in the following episode , . In of " After Trek " , shown after " Choose Your Pain " , showrunners Gretchen Berg and Aaron Harberts mentioned that Cornwell is a psychiatrist by training , who is not only old friends with Lorca , but is assessing him as she supervises him , and is worried about him . When asked how Cornwell would handle Saru ' s " break from reality " in , Jayne Brook commented that the admiral would try to talk Saru down slowly rather than threaten to remove him from serving on his ship . Brook went on to say , " " I think that she would give him time . I think she ' s a measured person who gives people the space , or wants to give them the space , to heal , and to observe herself . I think she would observe him and give him time . " " ( )