https://www.youtube.com/watch?v=Lbfpjd6dK8s
Various shots of the harbour of Rio de Janeiro where the defences of the city are being prepared. Oil drums that form an antisubmarine boom are taken into the water. Surface mines lined up in store. Various shots of mines being put aboard mine layer. Several shots of mines being dropped near harbour for further prevention. Depth charge being laid - it explodes.