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Suicide-bombing allows explosives to be placed at or very close to a target, with the deliverer having considerable real-time initiative and scope for concealment. He or she can adapt to circumstances in matters of timing as well as any movement of and even the precise location of the target. Countermeasures such as blast-walls and surveillance systems can be circumvented or fooled.

At the core of the attack is almost always a volunteer who is dedicated, intelligent and knowledgeable of the objective and the vicinity. The commitment may stem from political, religious or ethnic identity - and the determination to complete the mission may be extremely high once the operation started. The huge impact of suicide-bombs has been well-known at least since 9/11, but major incidents occurred long before then.

A specific assault on Rajiv Gandhi by a member of the Tamil Tigers (LTTE) guerrilla group killed India's former prime minister and fourteen other people on 21 May 1991. The assassin, Thenmozhi Rajaratnam, had got close enough to garland Gandhi with flowers before activating his device.

In October 1995, the Sri Lankan army dislodged the LTTE from its core city of Jaffna in a costly and brutal campaign. A devastating response followed on 31 January 1996, when a suicide-bomber detonated a truck-bomb at the entrance to the central bank right in the heart of Colombo's business district. Many important buildings were destroyed or damaged, and almost 100 people were killed; flying debris took a huge toll of injuries, with around 1,400 affected (see "The asymmetry of economic war", 14 February 2008)

In the past ten years, most such attacks have been across the middle east and south Asia, but they almost all have those characteristics listed above. They are repeatedly effective and difficult to counter without very considerable resources.

The similarity with armed-drones is striking. Drones such as the Reaper have multiple air-to-surface missiles, can loiter for hours and are "flown" in real time by operators thousands of miles away. There is no risk to these people, no suicide factor. Drones may not have quite the precision potential of a suicide-bomber, and in the very final seconds before impact the missiles that are fired cannot be diverted or halted. They are also dependent on previous intelligence which may be faulty and, as with suicide-attacks, a target person may be accompanied by many others, including family members. Yet they are increasingly the weapons of choice (see "Drone warfare: cost and challenge", 23 June 2011).

The majority of armed-drone developments in the past decades has been American or Israeli but the degree of proliferation is quite remarkable, not leastacross Nato. Apart from extensive Israeli use, the main proponents in current conflicts have been the United States, with drones "flown" from Creech air-forcebase near Las Vegas, and the United Kingdom, with the operating base in the process of moving from Creech to RAF Waddington, south of Lincoln in eastern England, one of the main bases for the RAF's air-warfare centre (AWC).

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