Philip Evans said the complex caper hatched at a series of Friday night pub sessions was the "largest burglary in English legal history."
The goods were taken from safe-deposit boxes inside the basement vault over the holiday weekend.
Evans said the gang used sophisticated methods and meticulous planning to drill into the wall of the vault before ransacking 73 boxes.
Four men said to be ringleaders have already pleaded guilty to conspiracy to commit burglary. Four others are on trial at Woolwich Crown Court accused of involvement in the theft.
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Prosecutors said much of the planning was done on Friday nights at a pub, and that one of the plotters had been using the Internet to search for the best drill for the job for more than two years.
The choice of drill was important because they had to bore a large hole through 20 inches of wall to get into the vault. The planners took advantage of the long holiday weekend to work unnoticed in the jewelry district in the heart of London.
Police said some of the goods and cash have been recovered and some items were shown to the jury.
Evans said that "at best, approximately one-third of the value of property may have been recovered." He said that means a great deal of property stolen from Hatton Garden remains missing.