Comment by Nathanba

I don't think that the prospect of getting hit under battlefield conditions is the problem here because that's always the problem and the tunnel is supposed to be the thing that helps you avoid getting hit. Tunneling under battlefield conditions has also been a thing in military conquest of castles for a very long time. These days you don't really have to tunnel towards an enemy, you just have to create underground spaces for your missiles, aircraft, etc. and as safer bases so the situation is vastly easier.