A plaque in memory of police constables Angela Bradley, 24, Gordon Alexander Connolly, 23, and Colin Morrison, 38, was unveiled at the dedicated memorial at Jubilee Gardens near Gynn Square.
The three died along with Scottish holidaymaker Alistair Anthony during a winter storm in 1983.
Lancashire Police Chief Constable Chris Rowley, Deputy Police and Crime Commissioner Andy Pratt, Blackpool mayor Coun Kath Benson joined emergency service and civic representatives at the ceremony and Supt Chris Hardy of Blackpool Police, said: “
"Those three brave officers died trying to save a member of the public, which is the epitome of public service.
“We also remember that member of the public, Alistair Anthony, who tragically died during the incident.
“As one of the darkest in the history of Lancashire Constabulary it is imperative that we continue to remember those who lost their lives that day, and as a Constabulary we feel a great sense of honour and pride in being able to remember them and mark their sacrifice with a memorial service."
1. 40th anniversary of police drowning tragedy
A wreath is laid in memory of the three police officers who drowned off North Shore in January 1983. Pictures: Neil Cross. Photo: Neil Cross
2. 40th anniversary of police drowning tragedy
Some of those who attended the 40th anniversary ceremony of the police drowning tragedy at Gynn Square, Blackpool Photo: Neil Cross
3. 40th anniversary of police drowning tragedy
The new plaque unveiled in memory of police contables Angela Bradley, Gordon Alexander Connolly and Colin Morrison. Photo: Neil Cross
4. 40th anniversary of police drowning tragedy
Some of the floral tributes in memory of the officers who perished. Photo: Neil Cross
5. 40th anniversary of police drowning tragedy
Officers on horseback were among those in attendance at the 40th anniversary ceremony. Photo: Neil Cross
6. 40th anniversary of police drowning tragedy
The scene of the 1983 tragedy as it is today. Photo: Neil Cross