The April 20 explosion on an oil rig in the Gulf of Mexico that caused the largest environmental disaster in US history occurred because every single defense on the rig named Deepwater Horizon failed, The New York Times reported Sunday.

The newspaper, which undertook its own investigation of the blast that killed 11 rig workers and injured dozens of others, said some of the defenses were deployed but did not work, some were activated too late, and some were never deployed at all.

Communications fell apart, warning signs were missed and crew members in critical areas failed to coordinate a response, the report pointed out.

The result was paralysis, The Times said.

For nine long minutes, as the drilling crew battled the blowout, no warning was given to the rest of the crew, the paper noted.

For many, the first hint of crisis came in the form of a blast wave, according to the report.

The paralysis had two main sources, The Times said. The first was a failure to train for the worst.

The crew members, though expert in responding to the usual range of well problems, were unprepared for a major blowout followed by explosions, fires and a total loss of power, the report said.

They were also frozen by the sheer complexity of the Horizon's defenses, and by the policies that explained when they were to be deployed, the paper said.

One emergency system alone was controlled by 30 buttons.

The Horizon's owner, Transocean, the world's largest operator of offshore oil rigs, had provided the crew with a detailed handbook on how to respond to signs of a blowout, the report noted.

Yet its emergency protocols often urged rapid action while also warning against overreaction.

The fiery April 20 explosion toppled the giant rig into Gulf of Mexico.

The rig's collapse ruptured underwater risers, opening a torrent of oil that fouled environmentally fragile Gulf coasts for three months before it was finally capped.