Dramatic phone calls revealed tonight how the emergency services struggled to cope with the chaos sparked by the July 7 suicide bomb attacks.
Urgent conversations among key staff were played in public for the first time as the long-awaited inquests into the 52 people killed finally began.
They laid bare how London Underground officials were plunged into confusion as explosions rocked Aldgate, Edgware Road and Russell Square stations.
Transport staff were left in the dark as the blasts rendered CCTV systems useless, sent out a blizzard of automatic warning messages and left telephone systems overloaded.
Tube staff were still debating whether the rapidly unfolding tragedy was the result of a power surge or a terrorist attack at least 44 minutes after the first explosion.
Meanwhile, police were reporting bomb blasts and suspected deaths as the walking wounded staggered out of the stricken stations, covered in soot.
One detective at Aldgate declared a major incident, describing the scenes as "pandemonium" as Tube operators elsewhere denied there had been any explosions.
Pc Neal Kemp, another Aldgate officer, called his control room and said: "There is a bomb in a carriage 100 yards into the tunnel. I have multiple casualties, possibly fatalities."
Relatives of those killed more than five years ago wept in court as Hugo Keith QC, for the inquest, outlined how emergency services were delayed by a series of apparent blunders.
He said: "These calls reveal considerable difficulties in assimilating information that is coming in as clearly a very confused incident presented itself."
Coroner Lady Justice Hallett heard that the four bombers - Mohammed Sidique Khan, Shehzad Tanweer, Jermaine Lindsay and Hasib Hussain - committed mass murder with the intention of getting worldwide publicity.
Tanweer, Khan and Lindsay detonated their bombs at Aldgate, Edgware Road and Russell Square at around 8.50am before Hussain blew up a bus at Tavistock Square an hour later.
Their actions were labelled "merciless savagery" that "unleashed an unimaginable tidal wave of shock, misery and horror" for families and friends.
The inquest heard that the emergency response was marred by a series of failings that might have delayed urgent medical care to those underground. They included:
:: Staff at the London Underground co-ordination centre continued to tell colleagues the incident was not terrorist-related at 9.32am, 44 minutes after the first explosion;
:: The Piccadilly Line manager, based at Earls Court, could not make outgoing calls from 9am onwards because the telephone system was overloaded;
:: Firefighters waited for confirmation from Tube staff that power was off, despite a police officer placing his foot on the third rail at Aldgate;
:: Confusion over which direction the Algate train was facing, which part of it was damaged, and whether it was in Aldgate or Aldgate East;
:: Emergency services were sent to Praed Street, in Paddington, instead of Chapel Street, where Edgware Road station is located, and to Liverpool Street, not Aldgate;
:: One of the Tube's specialist response units was still stuck in traffic in Clapham, south London, at 9.40am, as it waited for a police escort.
Mr Keith said: "There are repeated references to explosions and a high degree of confusion because of the way information is received.
"But there is a considerable amount of time, from the time of explosion of the bombs to acceptance by staff at network control that they were bomb-related."
The inquests heard the terror cell might have abandoned a plan to commit mass murder 24 hours earlier, as Britain waited to learn if it had won the 2012 Olympic Games bid.
Ringleader Khan sent a text message to Tanweer at 4.35am on July 6, that read: "Having major problem. Cannot make time. Will ring you when I get it sorted. Wait at home."
The bomber visited Dewsbury Hospital with his wife, Hasina Patel, on July 5 because of complications with her pregnancy and she miscarried on the day of the attacks.
Mr Keith said: "It may have been that the attack was originally planned for a different day."
The opening day of the inquests heard details of how the bombers travelled to London King's Cross Thameslink from Luton after leaving Leeds at 4am.
One neighbour of their bomb factory in Alexandra Grove said six Asian males left in two vehicles, including a white car which has never been traced.
The inquest heard Lindsay received a parking ticket as he slept in his car while he waited at Luton station for the other three conspirators.
They used four "operational phones", which were not their personal handsets, and left a stash of bombs and a handgun in the boots of their cars.
Commuters described some of the bombers as "smiling and laughing and generally relaxed" as they made their way to the capital, while two tried to avoid eye contact.
They carried the deadly improvised hydrogen peroxide and pepper bombs in plastic bags packed into rucksacks alongside ice packs to help control the volatile substance.
Lady Justice Hallett was told CCTV captured the men emerging from the Thameslink station and descending into the Tube, although Hussain wandered off to buy a battery, possibly because his detonator was broken.
A man of his appearance approached a Tube employee and said he wanted to speak to the duty manager about something "very important", but disappeared.
A piece of paper recovered from inside Lindsay's passport mentioned journey times to the potential targets of Paddington, Westminster and Bond Street.
The inquest also heard an earlier reconnaissance trip on June 28 indicated Lindsay might have planned to travel to South Kensington, but changed his plan because of delays.
Earlier, Lady Justice Hallett was told the inquest will look at a huge amount of information from the largest investigation database ever created by the Metropolitan Police.
The five-month hearing will sift through information from police, MI5, other emergency services and witnesses, as well as CCTV, forensic and technical evidence.
The coroner said as much evidence as possible would be considered in public and no decision had been made on whether she would sit in secret when considering sensitive intelligence material.
There have already been a series of investigations into the 7/7 attacks, including major reports by the Parliamentary Intelligence and Security Committee and the London Assembly.
The inquests have a wide-ranging remit to examine whether the emergency services' response was adequate and whether MI5 and the police could have prevented the atrocities.
The inquests will continue tomorrow with evidence about the wrecked Tube trains and number 30 bus, including never-before-seen video footage.