These departures are expected to be on top of the normal mandatory retirements this year.

It was recently estimated that there are 14 such mandatory retirements (on reaching 60) among senior ranks, of superintendent rank up, this year. Some of these may have availed of the severance package, the final details of which are not yet available.

The exit of up to 50 senior officers comes amid major internal restructuring under the new policing model, which has sparked an unprecedented dispute between senior staff associations and the sitting Garda commissioner.

Commissioner Drew Harris is leading out the ambitious reform, which will involve a significant reduction in superintendents and a smaller reduction among chief superintendents.

The 36 departures under the severance package are believed to include eight chief superintendents, 26 superintendents, one assistant commissioner, and one senior civilian.

The combined loss of up to 50 senior officers would represent around a fifth of the 221 officers currently in those ranks (166 superintendents, 47 chief superintendents, and eight ACs).

Security sources said there hasn’t been such a clear out since the first Fianna Fáil government in 1932 or possibly since its foundation in 1922.

“Even if you just take the severance numbers, around 36, that scale of turnover has never been seen before,” said one senior source.

Mr Harris chose the people under the severance package after they formally applied for it.

The Government deal, which has an estimated cost of around €6.5m this year, will provide the officers with six months’ salary along with the normal pension entitlements and lump sum payments.

Half of the officers will go in April, and the other half in September.

Assistant Commissioner Pat Leahy, head of the Dublin Metropolitan Region, is taking the package, and due to go in April.

The Cobh man was in the final shake-up for the current commissioner position in September 2018.

Two other senior assistant commissioners going, Michael O’Sullivan (Security and Intelligence) and John O’Driscoll (Special Crime Operations), are leaving on mandatory retirement grounds, this month and June respectively.

All three departures are seen are major losses for the organisation.

Chief superintendents taking severance also include experienced officers such as Dominic Hayes (Kilkenny-Carlow), Dave Dowling (Garda National Immigration Bureau), Tom Maguire (Security and Intelligence), John O’Reilly (Cavan-Monaghan), and Lorraine Wheatley (Dublin South Central).

Another chief superintendent going on mandatory retirement, in June, is Brian Sutton, head of Special Tactics and Operations Command, who previously lead investigations into the Crumlin-Drimnagh feud during the 2000s.

The departure of three assistant commissioners brings their number down to five. A current competition to create a list for these vacancies is at its final round, with eight chief superintendents through.

It is thought to include Pat Clavin (Criminal Assets Bureau), Declan Daly (Protective Services Bureau), Christy Mangan (Louth), Paul Cleary (Roads Policing), Anne-Marie Cagney (Dublin East), Tony O’Donnell (HQ), and two officers from the PSNI.

While chief superintendent numbers are reducing under the operating model, the reduction may be less than originally thought.

With the promotions to AC and departures, there are expected to be vacancies at chief superintendent for some of the 10 superintendents currently on a panel for promotion. Top of that list is Supt John Gordon (Dublin South Central).

The Garda also continues to have a vacancy at deputy commissioner rank.