The ExCeL centre will host exhibitors from around the world
Demonstrations are expected as one of the world's largest arms fairs opens in London's Docklands later.
The biennial Defence Systems and Equipment International is due to take place amid tight security.
The Campaign Against the Arms Trade, which says the event perpetuates a "deadly trade", and other groups plan to stage protests around the capital.
DSEI spokesman Paul Beaver said delegates at the ExCel centre would be "going about their lawful business".
'Lives are blighted'
More than 1,000 exhibitors from 40 countries are displaying weapons and equipment at the four-day fair, organised by Clarion Events.
It is also expected to attract some 25,000 arms brokers.
Mr Beaver said the event was good for the UK economy and would ensure that members of the armed forces had access to the best possible kit.
He added: "The UK is at war and we need to make sure our soldiers are protected.
"In this country we probably have the toughest defence export regulations in the world."
CAAT is organising a series of protests around the capital against what it describes as an immoral trade.
Sarah Waldron, CAAT's Core Campaigner, said DSEI was the "starkest demonstration" of what was wrong with the government's support for the arms trade.
She added: "The government will be inviting human rights abusers, countries engaged in conflict and those with urgent development needs to shop for weapons.
"Huge profits will be made by arms companies, but the costs are borne by the UK taxpayer, and millions of people whose lives are blighted by the arms trade."
Activists from a separate group, Disarm DSEI, will hold another protest and warn they will target the banks and firms which invest in the industry.
The group also says it will not co-operate with police ahead of its demonstration.
Sophie Williams of Disarm DSEI said the public was "still not seeing proportionate policing" in the wake of the G20 demonstrations.
But a Scotland Yard spokeswoman said it was aware of "demonstrations where organisers have not been in liaison with us".
She added: "We would urge such groups to work with us so that we can proportionately police peaceful protest and minimise disruption to local people."