John Twomey, Peter Blake, Barry Hibberd and Glen Cameron are accused of taking part in a "professionally executed" £1.75 million hold-up at a Heathrow warehouse in February 2004.
The Court of Appeal ruled last year that the case should be heard by a judge alone because of the danger of jury tampering.
It is the first major criminal trial in England and Wales to be held without a jury, and is taking place at the Royal Courts of Justice.
As the case was about to open it was the judge, Mr Justice Treacy, who was formally put in charge of the defendants by the clerk of the court, rather than any jury.
Earlier during legal submissions Sam Stein QC, for Hibberd, remarked: "We are breaking history. This is the first time that a court has started a jury-less trial."
Twomey, 61, of New Milton, Hants, Blake, 57, of Notting Hill, west London, Hibberd, 43, of Shepherd's Bush, west London, and Cameron, 50, of New Milton, Hampshire all deny a series of charges including robbery and firearm possession.
As prosecution barrister Simon Russell Flint QC was about to open the case, the judge explained how he had decided to adapt the normal procedure by which juries are given responsibility for a case.
He said: "At this stage the defendants would have been put in the charge of the jury and, although it is not apparently a strict legal requirement that they are, I have asked the court clerk to adapt the normal formula and to put me in charge of the various counts on the indictment."
Then, instead of reading out all 18 charges as she would have done to the jury, the clerk simply asked the judge to confirm he had seen the indictment.
She then informed the judge that the defendants had pleaded not guilty and that it was in his charge to say whether they were guilty or not - the task usually given to jurors.
After this procedure, Mr Russell Flint began to set out the Crown's case.
He told the judge: "Nearly six years ago, on February 6 2004, a professionally-planned and professionally-executed armed robbery took place at the warehouse premises of Menzies World Cargo."
Mr Russell Flint said the armed robbers expected to net £10 million in the raid after one gang member misread a delivery manifest, and instead they managed to get away with £1.75 million in various currencies.
It is alleged that each of the defendants were among the six robbers who entered the depot, wearing masks, high-visibility jackets and dark woollen hats.
Firearms were used to threaten the 16 members of staff, who were then tied up, the judge was told, one of them shot at, allegedly by Blake, as he tried to escape before being overpowered.
Mr Russell Flint said police had been aware since July 2003 that "something was going to take place" at the depot and kept watch on those they suspected of being involved.
He said the gang were equipped with "inside information" from those who "worked or had worked in and around Heathrow Airport".
In June last year Lord Judge, sitting with two other judges, agreed to set aside the "hallowed principle" of trial by jury because of what he described as the "very significant" danger of jury tampering.
The landmark decision was made under new powers in the Criminal Justice Act 2003.
There have already been three Old Bailey trials in the case, which is thought to have cost the taxpayer £24 million.
The latest proceedings ground to a halt in December 2008 after claims of jury tampering, after which prosecutors applied for a new trial, to be heard by a judge sitting alone.
Before the trial began today a small group of protesters gathered outside court holding up banners such as "No Jury = No Justice".
The trial was adjourned until tomorrow
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