Paris was an attack waiting to happen. Ever since the Charlie Hebdo outrage and the associated supermarket massacre in the same city earlier this year it seemed that it was not a matter of if but when. Paris is a large open city with a diverse population and although increased security measures had been put in place – armed soldiers are now a familiar sight outside synagogues and public buildings – it was clear that not every place was free from the threat of terrorist attack. It was the old story that those who guard everything end up protecting nothing.

On a mild November evening with crowds attending an international football match between France and Germany and a rock concert at the Bataclan concert hall, not to say those enjoying café society on a Friday night, Paris was an open city (as any enlightened European capital should be). For a brief moment it could be forgotten that France is a leading player in the global confrontation with radical Islam. French forces have been in action against Islamic terrorists in Mali and French aircraft are currently flying against Islamic State targets in Syria. That gave the terrorists both a reason and an opportunity to attack unprotected civilians using their weapons of choice – automatic assault weapons, grenades and explosive belts.

Against that kind of armoury security forces are always going to be hobbled but there is a means of fighting back. As was shown by the summary execution of the IS fighter known as “Jihadi John” who was killed in a drone attack in the northern Syrian town of Raqqa the battle is not a one-way street. In this instance the west not only had the technology to carry out the mission but it also had the intelligence information to plan it. This refers not just to communications interceptions but also to human intelligence, the best means being the “eyeball”.

In the fight against terrorism intelligence gathering remains paramount – the ability to watch the opposition 24/7, to give them no hiding place and to ensure that their every movement is monitored and that nothing is missed.

Inevitably questions will asked of the French security forces why this kind of intelligence was not available to forestall Friday’s attacks. Much will depend on the identity of the terrorists and it is already becoming clear that they were either Muslims or supported the Islamic State.

If they were French born and bred – not an impossibility given France’s large Islamic community – then those questions will have to be asked rigorously as clearly mistakes would have been made. However, if they were recent newcomers to France, then they would have come in “under the radar” and might not have become known to French security. Without hard information of that kind it is impossible to come to any conclusion.

What does seem to be the case is that the French security forces acted quickly to the crisis. In common with other intelligence services around the world they had been expecting an attack on a major city and understood the necessity of rapid and decisive action.