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Photo's from Jim Baumann 

Grillo and her four sisters;  these  innovative torpdeo launching  vessel had  toothed  'tracks'   to allow them to scale the 5 net barriers  at the mouth of the harbour at Pola so that the Italian Navy could  lauch an attack  on the  austro Hungarian battleships stationed there in 1918, numerous attempts were made, all failed due  to various  technical or weather problems. Grillo succeded in breaching 4 of the barriers before being discovered in searchlights and sunk by gunfire in 60 metres of water.