意思是：
战争即将结束时,他受了伤,被送进医院,脱离了所在部队.
having been wounded完成时的被动语态,having 的ing 是因为after的存在,为了取消句子的独立性.
towards the end of the war 在战争结束前
had been sent 过去完成时,被送到医院
was separated -----be + 形容词,separated意思是：分开的
主句是he had been sent to hospital and was separated from his unit.
after having been wounded towards the end of the war这半句表时间,在语法里叫前置时间状语从句?（不确定,我一般不关心语法）
回答补充：
had been sent 是过去完成时,表示过去发生的事情,强调对更接近现在的过去发生的影响.
had been sent to hospital（被送往医院）对更接近现在的过去的影响是was separated fron his unit.（脱离部队）,2者有先后和因果关系.
简单来说,“被送往医院”在“脱离队伍”前,并且对“脱离队伍”构成原因（影响）,所以前面用过去完成,后面用一般过去.