Try this as a hit EH on a Tiger tank:
requiredVersion "1.91"
private ["_victim","_shooter","_damage","_currDmg","_newDmg"]
?(count _this != 3): exit
_victim = _this select 0
_shooter = _this select 1
_damage = _this select 2
?!(typeof _shooter == "88"):exit
_currDmg = damage _victim
_newDmg = _currDmg + 0.3
_victim setDamage _newDmg