Police with machine guns are patrolling the Farnborough International Air Show amid the tightest ever security at the event.
Exhibitors from 32 countries are showing the latest technology
Around 300 officers, some of them armed, have been deployed at the air show, where 32 countries are exhibiting.
The event at Farnborough Aerodrome is expected to attract 300,000 visitors.
Protesters left an £888m cheque at the gates, to show what they say is the UK government's subsidy to arms companies.
A display from the Red Arrows opened the week-long event on Monday.
Defence giants BAE Systems, Airbus, Boeing and Rolls-Royce are among companies displaying their latest technology at the show, which is organised by the Society of British Aerospace Companies.
Economists are predicting healthy trade for exhibitors in the current climate of increased defence spending in the wake of September 11.
Highlights include a daily air display of up to 200 aircraft, flight simulators and a space pavilion.
Later in the week there will also be an airborne celebration honouring Rolls Royce to mark 100 years since the meeting of its founders, Charles Rolls and
A temporary town complete with roundabouts and roads has been built ahead of the event, which organisers say may be the biggest of its kind in the world.