It may be high on every terrorist agenda, but getting close enough to sink a vessel in the critical east-west waterway will not be easy.

Egypt rakes in around US$5 billion a year from shipping passing through the Suez Canal. That is a great incentive for keeping the vital Asia-Europe waterway open, but it may be a big ask for a military already stretched in imposing a state of emergency.

For most of its 193 kilometres, ships sail in single file up and down the canal that is just 202 metres wide. For a ship to be sunk at almost any point along the canal would block the route and create massive disruption to the world’s busiest sea trade.

Security in the Gulf or Aden and the Red Sea has been a priority for shipping since pirates began harassing cargo ships in the last decade, but the Suez was relatively peaceful until the weekend. Panamanian-registered container ship Cosco Asia came under fire in a northern section of the canal on Saturday, with the Suez Canal Authority saying a rocket propelled grenade had been used in the attack along with assault rifles.

Three people were arrested but no one knows if they were acting alone or as part of a terrorist group. Authorities regard that as an import distinction, but it is hard to see why. Any terrorist group leader with half a brain would have sinking a ship in the Suez Canal at the top of his list of priorities.

It would seem to be a relatively simple task with a targeted vessel just 100 metres away with nowhere to hide. So why has there been no real attack up to now, beyond Saturday’s minor adventure?

Hitting a giant cargo ship hard enough to sink it would require a suicide boat attack, floating mines or at least a missile or two. A small boat attack is out, as are dropping mines, and a rocket attack would mean setting up a battery on the banks of the canal.

With long, sandy stretches of wide open nothing, finding a spot would not be too difficult. But the difficulty will lie in staying undetected from spy satellites, drones and other electronic surveillance devices that make the area one of the most monitored in the world. A quick glance at Google Earth will also reveal that there are several military airfields in the Sinai Desert within easy striking distance of any Suez target.

So a terrorist attack in the Suez Canal serious enough to sink a ship and close the waterway may be an ever-present danger, but it will be extremely difficult to pull off.

A bigger threat is more likely to come from the political turmoil in Egypt. If it spills out of control, one faction or another could decide to blockade the canal to make a point or force some kind of action.

Ships will have to sail around Africa, and while the port of Durban may benefit from the increase in passing trade, the extra voyage costs will make it an expensive detour for cargo owners.