The two sides engaged in a desperate, life-or-death struggle.
Tips
usage
殊死 is a formal or literary term usually modifying words like 搏斗 (struggle), 抵抗 (resistance), or 战斗 (battle) to mean the fight is desperate and life-or-death. Historically, 殊死 also referred to beheading as a form of capital punishment.
memory
殊 means 'special or different' and 死 means 'death' - a 'special death' situation, i.e. a do-or-die moment.