phone ▁can ▁be ▁produced ▁from ▁a ▁low - cost ▁om n id irection al ▁type , ▁but ▁must ▁be ▁used ▁while ▁station ary , ▁as ▁the ▁reflect or ▁imp edes ▁its ▁movement ▁through ▁water . ▁A ▁new ▁way ▁to ▁direct ▁is ▁to ▁use ▁a ▁spher ical ▁body ▁around ▁the ▁hydro phone . ▁The ▁advantage ▁of ▁direct ivity ▁spher es ▁is ▁that ▁the ▁hydro phone ▁can ▁be ▁moved ▁within ▁the ▁water , ▁r idd ing ▁it ▁of ▁the ▁inter ferences ▁produced ▁by ▁a ▁con ical - sh aped ▁element . ▁ ▁Array s ▁Multiple ▁hydro ph ones ▁can ▁be ▁arranged ▁in ▁an ▁array ▁so ▁that ▁it ▁will ▁add ▁the ▁signals ▁from ▁the ▁desired ▁direction ▁while ▁subtract ing ▁signals ▁from ▁other ▁directions . ▁ ▁The ▁array ▁may ▁be ▁ste ered ▁using ▁a ▁beam former . ▁ ▁Most ▁commonly , ▁hydro ph ones ▁are ▁arranged ▁in ▁a ▁" line ▁array " ▁but ▁may ▁be ▁in ▁two - ▁or ▁three - dimensional ▁arrang ements . ▁ ▁S OS US ▁hydro ph ones , ▁laid ▁on ▁the ▁se ab ed ▁and ▁connected ▁by ▁under water ▁c ables , ▁were ▁used , ▁beginning ▁in ▁the ▁ 1 9 5 0 s , ▁by ▁the ▁U . S . ▁Navy ▁to ▁track ▁movement ▁of ▁Soviet ▁sub mar ines ▁during ▁the ▁Cold ▁War ▁along ▁a ▁line ▁from ▁Green land , ▁I cel and ▁and ▁the ▁United ▁Kingdom ▁known ▁as ▁the ▁G I UK ▁gap . ▁These ▁are ▁capable ▁of ▁clearly ▁recording ▁extremely ▁low ▁frequency ▁in fr as ound , ▁including ▁many