The IKS Ya'Vang was a Klingon warship of the Dominion War to which Worf's son Alexander was reassigned from the Rotarran in 2374, prompting Worf and Jadzia Dax to bring forward their wedding.
The Ya'Vang is mentioned in the Deep Space Nine episode You Are Cordially Invited, set just after the Federation retakes the station. Alexander Rozhenko, who had enlisted in the Klingon Defence Force and joined the crew of the Rotarran in Sons and Daughters, receives orders transferring him to the Ya'Vang.
Because the ship is to leave within days, Worf and Jadzia decide to marry at once so that Alexander can stand beside his father at the ceremony. The rushed timetable leads to Jadzia's difficult trial under Sirella, the mistress of the House of Martok.
The ship itself is not seen on screen.