Emergency services are descending on Portsmouth’s naval base today for a massive exercise.
People are being told not to panic if they see a large number of emergency vehicles in the area.
All three services will be putting their skills to the test in an event called Exercise Cameron.
They are using the naval base as the focus of the exercise.
The base was chosen because they can simulate an inner city environment there.
Chief Inspector Clive Marsh, who leads on chemical, biological, radiological and nuclear issues for the police force, is directing the exercise.
He said: ‘We are gathering to put our offices and staff through their paces and ensure we are effectively prepared for any potential contingency.
‘Our message to anyone who sees the vehicles and officers gathering is not to be alarmed.
‘It is simply an exercise to make us better prepared for any eventuality.
‘All agencies taking part on the day are committed to ensuring we can provide an excellent response to such risks and this exercise provides us with a rare opportunity for all involved to rehearse our response together.’