A demonstration has been planned against Boris Johnson's purchase of a water cannon.
Metropolitan Police have bought three machines from the German police.
London mayor Boris Johnson ordered the cannons before home secretary Theresa May decides whether to authorise their use.
As a protest, Class War, an activist group, has organised 'Operation Supersoaker' for August 30 in Gravesend.
Spokesman Ian Bone said: "Johnson has bought three second hand water cannons which are shortly to be installed at the Met Police training centre in Gravesend.
"At present it is not even legal to use them on the streets because Theresa May has not approved.
"But why wait – let’s get our retaliation in first.
"There are misgivings in Gravesend about having the water cannon there. Some fear it will attract troublemakers. It has. Us."
The machines have never been used in Britain.
Mr Bone added: "Thousands will flood into Gravesend to take on the water cannon.
"We can finish them off by a daring pre-emptive attack."
The Met has said the cannons will not be used unless authorised by the government.
It is understood the cannons will receive "several weeks" worth of work include fitting CCTV and adaptations to bring them in line with those used in Northern Ireland.
Don't miss out, subscribe today. Keep up to date with our newsletters.
A guide for your future. For year 11 students in Kent and Medway. Click here for the e-edition.
Education, Training & Childcare is a special supplement published by KM Media Group four times a year. Click here for latest e-edition.
Get the latest food and drink news, recipes from some of the nation's top chefs plus updates from Kent's vineyards and breweries.
Search in your local area to find your perfect partner in Kent, with FreshStart Dating! PLUS, register for free!.
Find out what's going on in the garden, with Kent expert Lucy Hewett's weekly update.
Buy pictures that you've seen in a KM newspaper, or send in a picture and we will place it on our photo sales website so that you can purchase a super, unique gift.