It was mandated by the Def Stans that the Hercules fuel system was to be protected against a table of threats (including small arms fire). The options open to IPTL and DA were to fit ESF or Inerting Gas. It had neither and so, by definition, the Herc (all marks) was not airworthy in this respect. The MoD did not contend this assertion in court.
This situation remained extant until all ac were eventually made safer by the fitting of ESF post the loss of XV179 - many years after it should have been done and too late for some of my friends. Also, it is arguable that the MoD did not meet their obligations because they realised that the ac was unsafe and did not meet the regulations but beacause they had to be pushed into action by public pressure.