The 33-year-old, who admitted to killing 69 people on the island, calmly told prosecutors "my aim was to kill" and that he hoped to scare the rest into the water to drown.
Breivik said he planned to murder the former prime minister Gro Harlem Brundtland, who was visiting the island, video her execution and post it on the internet.
Families and survivors heard how Breivik had also hoped to detonate three car bombs in Oslo targeting government and media buildings with huge loss of life.
He hoped the bomb in his van would collapse the building that housed the prime minister's office, killing the prime minister and the entire government.
In the end his single car bomb in the government quarter on July 22 killed eight people and injured hundreds more.
:: Breivik Trial: Live Updates
He blamed journalists for his "horrible" actions saying they had prevented him from spreading his message.
After hearing from Breivik about his plans for Utoya the prosecution requested a break in proceedings with people openly crying in court.
The detail and full scale of the Norwegian killer's plans were revealed on the fourth day of his trial for the attacks that killed 77 people and injured hundreds more in Norway last summer.
Breivik admits to all of the killings, but pleads not guilty to terrorism on the grounds he acted in self-defence to stop the spread of Islam.
The key issue of the trial is whether Breivik can be established as criminally insane.
What the five judges decide will dictate whether he will spend the years to come in a prison cell or on a psychiatric ward.
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More to follow...