Forty-two defenders were killed and 162 were wounded in the offensive which helped restore rail and road connections between Zagreb and eastern Slavonia.
The liberation of occupied territory resumed in August 1995 with Operation Storm and ended on January 15, 1998 with the peaceful reintegration of the Danube River Region.
Addressing members of the army and police, participants in Operation Flash and the public, Parliament Speaker Boris Sprem said the operation was a landmark in Croatian history which Croatia remembered with pride.
He said the operation "showed the unity and determination of Croatian citizens to crush, in a legitimate liberation war, the armed rebellion against the Croatian state and liberate their own territory."
Sprem said Flash marked the start of the dismantling of former Yugoslav President Slobodan Milosevic's policy of hegemony and aggression founded on demagogy and propaganda. "The military and police Operation Flash was also the critical point in the Homeland War which convinced the international community of the justness and legitimacy of Croatian goals as well as of the destructiveness of Milosevic's policy of aggression."
Sprem said the operations "Flash and Storm, and the subsequent reintegration of the Danube River Region, are the pillars of the present-day Croatian state."
"The military determination in the defence of one's own country and the protection of one's own rights as well as the political willingness for cooperation, dialogue and co-existence in peace, tolerance and mutual respect, all that is condensed in those critical events which eventually enabled the normal functioning of the Croatian state within its internationally recognised borders. Those are also the basics of Croatia's state policy from which there is no deviation," said Sprem.
After state officials laid wreaths at a monument to Croatian defenders, military ordinary Juraj Jezerinac celebrated a memorial service.
Asked by the press to comment on the absence of Prime Minister Zoran Milanovic, Deputy Parliament Speaker Jadranka Kosor said this was the first Flash anniversary since he stepped into office and that he should have come to pay his respects to the victims.