▁area . ▁ ▁World ▁War ▁I ▁for ▁USS ▁A ro ost ook – 1 9 1 8 ▁ ▁After ▁a ▁brief ▁sh aked own ▁cru ise ▁in ▁mid - J une ▁ 1 9 1 8 , ▁A ro ost ook ▁took ▁on ▁board ▁a ▁load ▁of ▁mines ▁and ▁then ▁began ▁a ▁voyage ▁across ▁the ▁Atlantic ▁Ocean ▁in ▁the ▁company ▁of ▁her ▁sister ▁min el ayer , ▁USS ▁Shaw mut . ▁This ▁voyage , ▁a ided ▁by ▁the ▁novel ▁technique ▁of ▁ref uel ing ▁at ▁sea , ▁took ▁her ▁to ▁Scotland , ▁where ▁in ▁July ▁she ▁participated ▁in ▁lay ing ▁the ▁North ▁Sea ▁Mine ▁Bar rage , ▁lay ing ▁thousands ▁of ▁mines ▁across ▁the ▁mouth ▁of ▁the ▁North ▁Sea ▁in ▁order ▁to ▁create ▁a ▁bar rier ▁for ▁German ▁U - bo ats ▁trying ▁to ▁depart ▁from ▁German ▁se ap ort s ▁to ▁the ▁open ▁Atlantic . ▁ ▁A ro ost ook ▁laid ▁a ▁total ▁of ▁ 3 , 1 8 0 ▁mines ▁in ▁this ▁operation : ▁ ▁plant ed ▁ 3 2 0 ▁mines ▁during ▁the ▁ 3 rd ▁min el ay ing ▁exc urs ion ▁on ▁ 1 4 ▁July , ▁ ▁plant ed ▁ 3 2 0 ▁mines ▁during ▁the ▁ 4 th ▁min el ay ing ▁exc urs ion ▁on ▁ 2 9 ▁July , ▁ ▁plant ed ▁ 2 9 0 ▁mines ▁during ▁the ▁ 5 th ▁min el ay ing ▁exc urs ion ▁on ▁ 8 ▁August , ▁ ▁plant ed ▁ 3 3 0 ▁mines ▁during ▁the