Why are you so sure that the Vanguard wouldn’t have access to such a basic technology as ultrasound (never mind a futuristic improved version). Why do you believe that, following the events of the red war that the Vanguard would end up in the same tower as the black armory ? That in addition to such a coincidence the Vanguard would fail to secure their new home ? Why do you not consider the fact that the black armory would have detected the first Vanguard recon team on approach to check the tower and would have made every effort to ensure it wasn’t suited as their new home ?