The fact that bombers have managed to breach high security at Palace Barracks will be profoundly worrying for the PSNI, the British Army and MI5, which has its headquarters on the site.
Police have confirmed an explosion took place inside a postal van at the base in Holywood, Co Down around 10.30am yesterday.
It is believed an incendiary device detonated, causing an intense fire which destroyed the van, two other cars and three nearby garages.
Fortunately, the driver was not inside the van at the time and there were no injuries as a result of this attack.
The suspicion is that dissident republicans were behind this firebombing and they will be satisfied they have managed to undermine defences at this heavily fortified military base.
There are serious questions for the army in terms of how a van carrying any sort of lethal device managed to gain access to this complex.
Certainly, the public perception would be that given the ongoing activities of dissident groups, any barracks - particularly one housing the intelligence services - would be subject to the most stringent security.
As we know, dissidents have attacked Palace Barracks in the past. In 2010, a bomb in a hijacked taxi was abandoned outside the base and exploded as the surrounding area was being evacuated.
In 2009, two soldiers, Patrick Azimkar and Mark Quinsey, were shot dead outside Massereene Barracks in Antrim as they collected a pizza delivery.
Any breach of security at a base - which is an obvious target for dissidents - is clearly alarming.
This incident also raises concerns over Royal Mail security which has systems in place to detect letter bombs.
Obviously, security will have to be reviewed as a result of this attack but there will be many questions to be answered about how such a serious breach occurred at a high profile target.
