The purpose of the bulkhead is threefold: to seal the forward end of the motor, to retain the pyrogen igniter, and to act as a blowout plug in case of motor overpressurization (discussed earlier).
It's a threefold increase on the figure for October when Iraqi forces launched a major assault to retake the city of Mosul, the last major stronghold in Iraq of the Islamic State group.
Me from myself thy cruel eye hath taken, And my next self thou harder hast engross'd: Of him, myself, and thee, I am forsaken; A torment thrice threefold thus to be cross'd.