Frogmen can swim in deep waters and fight through strong currents to get to their objective. The Undertows take that advantage one up with being equipped and willing to swim in the foulest water environment imaginable. They go where normal frogmen don't go which are polluted harbor bays, industrial waste water and the sewers. They wear non-corrosive, near-hermetically sealed wet-suits and they undergo special anti-infection shots that gives them some immunity from all but the strongest pathogens.