"A character using a shield increases their effective Melee (unarmed) skill by one level when parrying. A character with no Melee counts as having Melee 0 when using a shield to parry."
That is, if I have Melee (blade) 1 and Melee (unarmed) 0, then I can already parry for one point using my sword, and there's no reason to use the shield. And if I have no levels in Melee (unarmed), then raising it to 0 does me no good for parrying, since parrying means subtracting my skill level from my opponent's attack roll.
Not that a sci fi game like Traveller has to account for every aspect of Low Tech combat. But I want to strand the PCs on a primitive planet
