Four men were killed and one woman injured when a gunman went on a rampage through Darwin's CBD on Tuesday before the suspect was arrested by police.

It was a crime that shocked our nation and for that, at least, we should be grateful.

Australia's reaction to Tuesday's shooting shows this country is not yet immune to the enormity of such tragedies.

When four people are gunned down, even in a city as remote as Darwin, it still send shockwaves through the rest of us.

And that's exactly how it should be - even if it's not the case in every country.

We are told that shootings such as this have become so commonplace in the USA that many go unreported outside of the immediate vicinity.

The dead must number in double figures or the gunman must open fire in a school for the rest of the country or even the rest of the world to take notice.

It beggars belief, and it's a country we never want to become.

Tuesday's mass shooting in Darwin coincided with the launch of Operation Armour by NSW Police, focused on preventing, disrupting and reducing firearm thefts.

Deputy Commissioner Gary Worboys told the launch in Tamworth that the theft and sale of firearms often occurred in regional areas.

"When in the wrong hands, firearms are dangerous and a threat to the community. We will continue to do everything we can do to keep the public safe," Deputy Commissioner Worboys said.

The police operation represents another proactive step towards reducing gun violence and keeping guns out of the hands of criminals.

These operations can never be 100 per cent successful but, as the Australian experience since Port Arthur has proved, fewer guns does mean fewer mass shootings.

The mass shooting in Darwin on Tuesday night should not deter us from continuing to exercise stringent gun control in this country. Rather, it should highlight just how rare such shootings have been in the past 20 years.

We grieve for the victims of Tuesday night's outrage, but we honour their memory by continuing the fight to reduce the chance of it happening again.

And we vow to never become a country where mass shootings fail to shock.