A Senate investigation of the January 6 insurrection at the US Capitol has uncovered broad government, military and law enforcement missteps before the violent attack.

Those errors included a breakdown within multiple intelligence agencies and a lack of training and preparation for Capitol Police officers who were quickly overwhelmed by the rioters.

The Senate report released on Tuesday is the first, and could be the last, bipartisan review of how hundreds of former president Donald Trump’s supporters were able to violently push past security and break into the Capitol that day, interrupting the certification of President Joe Biden’s victory.

It includes new details about the police officers on the front lines who suffered chemical burns, brain injuries and broken bones and who told senators that they were left with no direction when command systems broke down.

It recommends immediate changes to give the Capitol Police chief more authority, to provide better planning and equipment for law enforcement and to streamline intelligence gathering among federal agencies.

As a bipartisan effort, the report does not delve into the root causes of the attack, including Mr Trump’s role as he called for his supporters to “fight like hell” to overturn his election defeat that day.

It does not call the attack an insurrection, even though it was.

And it comes two weeks after Republicans blocked a bipartisan, independent commission that would investigate the insurrection more broadly.

“This report is important in the fact that it allows us to make some immediate improvements to the security situation here in the Capitol,” said Michigan Senator Gary Peters, the chairman of the Homeland Security and Governmental Affairs Committee, which conducted the probe along with the Senate Rules Committee.

“But it does not answer some of the bigger questions that we need to face, quite frankly, as a country and as a democracy.”

The House in May passed legislation to create a commission that would be modelled after a panel that investigated the September 11 terrorist attack two decades ago.

But the Senate failed to get the 60 votes needed to advance, with many Republicans pointing to the Senate report as sufficient.

The top Republican on the Rules panel, Missouri Senator Roy Blunt, has opposed the commission, arguing that investigation would take too long.

He said the recommendations made in the Senate can be implemented faster, including legislation that he and Minnesota Democratic Senator Amy Klobuchar, the rules committee chairwoman, intend to introduce soon that would give the chief of Capitol Police more authority to request assistance from the National Guard.

The Senate report recounts how the Guard was delayed for hours on January 6 as officials in multiple agencies took bureaucratic steps to release the troops.

It details hours of calls between officials in the Capitol and the Pentagon and as the then-chief of the Capitol Police, Steven Sund, desperately begged for help.

It finds that the Pentagon spent hours “mission planning” and seeking multiple layers of approvals as Capitol Police were being overwhelmed and brutally beaten by the rioters.

It also states that the defence department’s response was “informed by criticism” of its heavy-handed response to protests in the summer of 2020 after the death of George Floyd at the hands of police.

The senators are heavily critical of the Capitol Police Board, a three-member panel that includes the heads of security for the House and Senate and the Architect of the Capitol.

The board is now required to approve requests by the police chief, even in urgent situations.

The report recommends that its members “regularly review the policies and procedures” after senators found that none of the board members on January 6 understood their own authority or could detail the statutory requirements for requesting National Guard assistance.

Two of the three members of the board, the House and Senate sergeants at arms, were pushed out in the days after the attack.

Mr Sund also resigned under pressure.

Congress needs to change the law and give the police chief more authority “immediately”, Ms Klobuchar said.