Over two years since the publication of the Patten report, which proposed sweeping changes to the RUC's name, badge, structure, ethos and recruitment procedures, Sir Ronnie Flanagan said yesterday was a day of "mixed, often difficult" emotions for him and his officers.
"At this time of annual remembrance I think, of course, of our widows, our bereaved families, our disabled officers.
"This is a difficult weekend for them. But I'm feeling overwhelmingly proud this morning, very proud to have been the Chief Constable of the Royal Ulster Constabulary, very proud now to be Chief Constable of the new Police Service of Northern Ireland (PSNI) and to see later this morning our new trainees who start an entirely new training programme to bring about hopefully a more peaceful future for all of the people of Northern Ireland," he told the BBC's Breakfast with Frost.
The new trainees are being recruited from both communities on a 50:50 basis in an effort to redress the dominance of Protestants - they made up 92 per cent of the RUC - in the new service.
The new 19-strong Police Board, the PSNI's watchdog body, also assumed its powers yesterday.
It will be up to the board to decide on the new crest and symbols for the new service.
Its cross-community make-up, however, has given rise to fears that members will be unable to reach agreement on these issues, possibly deferring the ultimate decision on them to the British government.
Sinn FΘin is the only one of the North's main political parties which has so far failed to endorse the new service.
Sir Ronnie yesterday said he was confident republicans would eventually take their seats on the board as well as join the PSNI.
"It will have to happen and they have to grasp their responsibility because they have to realise that it is only through full support from people with totally differing views that policing can truly be enhanced to the degree that it should."
In response, Sinn FΘin's Education Minister, Mr Martin McGuinness, said his party's refusal to take up its two seats on the board was in line with the feelings of a majority of nationalists.
The onus was on the British government to amend policing legislation to bring about a "truly new beginning" to policing, he added.
Meanwhile, the British Prime Minister, Mr Blair, has paid tribute to the "courage, sacrifices and professionalism" of the RUC, saying the force had directly contributed to creating a more peaceful society in Northern Ireland.
Mr Blair also praised the way in which serving officers had embraced change.
In a letter to Sir Ronnie he wrote: "The courage, sacrifices and professionalism of the men and women in the RUC and their support staff, and their families will not be forgotten."
Mr Blair said he understood that yesterday would have been regarded as a sad day by some in the service.
"I hope, however, that it will also be seen as a proud day. A day both to reflect on the achievements of the past and to look to a new beginning to policing.
"To a service which is gaining the widespread community support and the further enhancement to its wider reputation that it undoubtedly deserves."
Sir Ronnie said he was pleased the British Prime Minister had recognised the "professional and unstinting service which the RUC has rendered to all of the people of Northern Ireland during its proud 79-year-history", adding: "The bravery, dignity and resolve which police officers, their civilian colleagues and their families have displayed in the darkest of times are qualities which I firmly believe will endure into the Police Service of Northern Ireland."