"Once More Unto the Breach" is the 157th episode of the television series Star Trek: Deep Space Nine, the seventh episode of the seventh season. The title is taken from one of the more famous speeches in Shakespeare's play Henry V.
An aging and increasingly senile Dahar master Kor has lost influence in the Klingon Empire. He comes to DS9 to ask Worf for help in securing a starship command, and a chance to die in battle. Worf brings the request to General Martok, who is planning a raid deep into Cardassian space with five Birds of Prey. Martok angrily rejects the request. Kor once rejected a young Martok's application to become an officer based on Martok's lower class lineage; the general still holds the grudge. As a compromise, and not aware of Kor's poor mental health, Worf appoints Kor as the third officer of the Ch'tang, Martok's ship.
Once aboard, Kor recounts old war stories to a crew enthused with having a living legend among them. However, this changes after the first battle when Martok and Worf are temporarily incapacitated and Kor is forced to take command. Kor's senility causes him to relive an old battle and give inappropriate commands. Disaster is averted when Martok and Worf recover and resume command.
Kor's pride is severely hurt as Martok and much of the crew mock him. Worf is forced to remove the Dahar master from duty, but blames himself for placing Kor in an untenable situation. Martok also realizes mocking Kor has brought him no pleasure. The pair agree to appeal to Chancellor Gowron to find a worthy and suitable place for Kor.
As the cloaked Klingons return to friendly space, they discover ten Jem'Hadar ships are in pursuit and will intercept them before they reach safety. Worf prepares to embark on a suicide mission in one Bird of Prey to delay the pursuers, and allow the remaining ships to escape. Kor learns of Worf's plan from Darok, an old Klingon who is Kor's age and is sympathetic to his plight. Kor's pride is rekindled when he realizes only his lifetime of experience can make the plan work. It is also the warrior's death he has longed for. As such, the Dahar master surprises Worf with a hypospray, sedates him and takes his place. However, before Kor transports out, he tells Worf that when he reaches the halls of the honored dead, he will find Jadzia Dax and tell her that Worf still loves only her and that he brings her honor everyday.
Martok and his crew observe the battle from the Ch'tang's bridge. Martok belatedly discovers Kor's actions when Worf joins him. Against the odds, Kor succeeds in delaying the Jem'Hadar. An incredulous Martok is the first to toast Kor's noble end, and the crew sing to Kor's victory.