One of the world's largest arms fairs, the biennial Defence Systems and Equipment International (DSEI), has opened in London amid tight security.
WORLD ARMS TRADE
Top exporters 2004
United States: $18.5bn
Top importers 2004 (developing nations only)
United Arab Emirates: $3.6bn
Saudi Arabia: $3.2bn
Source: Defence Analysis Dept, International Institute for Strategic Studies/ US Congress
More than 1,200 firms from 34 countries are displaying weapons and equipment for army, navy and air force use.
The event prompted demonstrators to hold a march in protest at UK government invitations for countries accused of human rights violations.
The UK is the world's second largest arms exporter after the US.
Russia and the Ukraine are third and fourth on the list of top weapons exporters, ahead of France at number five.
The UK's Ministry of Defence has invited delegations from 61 countries to the event.
They range from uncontroversial choices like Germany and the United States to states like China, Indonesia and Saudi Arabia, which have been criticised for their human rights records.
For the first time a delegation from Iraq will be attending the arms fair.
Anna Jones, campaign coordinator for the Campaign Against Arms Trade, said the government was "welcoming the world's arms dealers and human rights abusers to do business in London" while Prime Minister Tony Blair was pushing for arms trade controls at a United Nations summit later this week.
Organisers expect some 20,000 visitors to come to the four-day event, which ends on Friday.
The UK's defence industry employs 345,000 people
Security is tight around the venue, with participants going through four ID checks before being allowed to enter. A heavy police presence surrounds the venue, with vans full of police on stand-by parked in roads nearby.
As the trade show started, uniformed officers from dozens of countries mingled with hundreds of representatives from the arms industry.
The trade fair showcases new technology for both military and civil use. Inside, exhibitors showcased their latest weapons systems - tanks, guns and ammunition - alongside other equipment like battlefield management software, field hospital kits and decontamination suits.
At the most recent fair two years ago the organisers asked exhibitors not to display controversial weapons like cluster bombs and equipment that could arguably be used for torture.
The list of exhibitors includes defence giants like BAE Systems, EADS, Thales and Lockheed Martin, alongside dozens of small and medium-sized companies.
DSEI is run by Spearhead Exhibitions in association with the UK's Defence Export Services Organisation, a part of the Ministry of Defence.
The respected medical journal The Lancet last week criticised its own publisher, Reed Elsevier, for being the owner of Spearhead Exhibitions.
In an editorial, The Lancet urged Reed Elsevier to sever all links with the arms trade, claiming they were incompatible with the journal's values.
"On behalf of our readers and contributors, we respectfully ask Reed Elsevier to divest itself of all business interests that threaten human, and especially civilian, health and well-being," the journal said.
Meanwhile, around 100 protestors marched from East Ham to meet their counterparts outside the event in Docklands.
James O'Nions, a researcher for the Campaign Against the Arms Trade said: "This fair is one of the world's largest and is subsidised by the British Government.
"Its purpose is to sell arms to countries all around the world, some of which have the worst human rights record."