A chain that runs from Green Island to Stonecutters Island

Hi everyone, 

I am a 78-year-old man born in 1942. I remember soon after the war was over - I was then still a kid, I saw something like a large oil-drums chained up one after another all the way from the Green Island on the HK side to the Stonecutters Island. No one seems to know what it was until one day a man told me it was for blocking ships from entering the harbour not only that there were metal curtains that hang down from drums to the seabed forming an iron curtain beneath the sea surface. The purpose of which is to stop submarine from sneaking through. 

Please tell me if anyone of you heard or actually have seen this chain. Or you think it is my illusion or I am making this up. I'm not because I remember quite clearly around that time, on the other side of the Green Island a Fat San Macau Ferry got sunken with the chimny sticking out of water. I was left there unsalvaged for a number of years.

I am a new member of Gwulo and I am not surprised if the above mentioned photos are already in the group. If that's the case, please let me know where to look for.  

Thank you 

 Richard Ling