The Minister for Justice is to introduce thousands of new prison space and toughen gun and drug laws in an effort to tackle serious crime.
Speaking at the annual conference of the Association of Garda Sergeants and Inspectors in Cork, Mr McDowell said a new 800-bed "super prison" on Spike Island, Co Cork, was planned.
He said there had been 28 offers of sites for the planned new 1,000-bed Mountjoy Prison, which will replace the existing Mountjoy facility as well as St Patrick's Institution and the women's Dochas Centre. The number of prison places is to be increased from 3,300 to 4,500.
Mr McDowell told delegates the plans were part of a major drive by the Government to tackle the rising threat posed by underworld and dissident republican gangs.
Mr McDowell said that he was determined to change the wording of 1999 legislation providing for a mandatory 10-year jail term for anyone caught with €12,500 or more worth of illegal drugs. Provisions for mandatory sentencing allowed a judge to put aside the 10-year term in exceptional sentences. But judges were invoking that too often.
"The exception has become the norm," he said. "The judges will have to realise that the use of guns is posing a very real threat to the future of an unarmed Garda force."
Guns and drugs were now inextricably linked, because major international drug cartels were including weapons in drug shipments being sent to Ireland, he said.
Mr McDowell expressed disquiet at the way the bail laws were being interpreted in the courts. Changes introduced following the bail referendum meant that suspects would be refused bail if a senior garda testified in court that there was a likelihood that the person would reoffend.