Europe's largest arms fair is taking place in London over four days. Below, a representative of the industry sets out why he thinks it's so important to the UK.
Hawk jets: Defence industry success story
Click on the link in the text for the view from the campaigners.
Major General Alan Sharman, director general of the Defence Manufacturer's Association:
Why do we need a defence industry? The fundamental raison d'etre is one of national security, to ensure we keep our own armed forces supplied with materials and services.
This is the case for the UK, as it is for other nations.
The UK particularly learnt this lesson when the source of a key piece of naval optical range equipment, Germany, suddenly became our enemy in 1914.
But the defence industry has also shown itself to help the development of other high technology industries because it is frequently at the forefront of innovation.
And so, successive governments have recognised the importance of the defence industry over the years.
So today, the UK has the world's second largest defence industry (as a percentage of GDP) employing some 345,000 people.
That's a significant proportion of the UK's total manufacturing workforce and output.
Half of all aerospace and shipbuilding jobs in the UK are defence jobs. Some 40% of the electronics industry is also part of the defence industry.
What's more, these figures don't take into account additional jobs dependent on defence spending. According to one calculation by Janes Information Group, that could be as many 1.5m jobs.
But this is also a highly diverse industry.
The UK's defence industry goes from aircraft, warships and armoured fighting vehicles, through communications, radars, propulsion, munitions and support services, to basic equipment such as clothing and on to financial and support activities.
But increasingly, British companies are taking this defence industry expertise into equipment for humanitarian relief, counter terrorism and peace keeping activities.
And since the terrorist attacks of 11 September 2001, the UK's world expertise in counter-terrorism has come to the fore.
But while the fundamental role of the defence industry is to supply our own armed forces, exports are vital for its survival.
The industry cannot be sustained by relying on the Ministry of Defence cheque book alone.
Crucially, profits from exports help to spread the cost of the UK's own research and development, meaning our defence budget is up to £400m less than it would be otherwise.
But most importantly, the defence industry is one of our great success stories because approximately 40% of its output goes to export, some £4.1bn in 2001.
We currently hold a fifth of the world defence market, placing us second only to the United States.
What is so impressive about this point is the industry has achieved this position in an environment where there are a large number of countries to which the Government will not allow the export of defence equipment.
Furthermore, the UK does not have a Government subsidised foreign military sales programme, unlike a number of its major competitors.
Defence exports benefit not just the British companies concerned, but also UK industry as a whole, as they can serve as a catalyst for national economic and technological development.