The U.K. currently spends 2.8 percent of its gross domestic product on defense, the second-highest proportion after the United States.

There can be no doubt that, with heavy involvement in Afghanistan as well as the demands of the Iraq situation, the British armed forces have been under severe strain. The military chiefs who have been calling for bigger budgets have found themselves in head-on opposition to their political masters. Instead of securing more funds, military leaders have been told to expect big cuts. A reduction of as much as 20 percent in the defense budget has been mentioned.

This is leading to an agonizing reappraisal of the U.K.'s military needs and, at a deeper level, the nature, purpose and role of armed forces in modern conflict. Being questioned in particular is whether mega-expensive projects planned years in advance that swallow up billions of pounds are the right way to provide national security.

For example, the U.K. has spent a fortune, and is planning to spend more, on super-performing aircraft designed originally for operation in the Cold War. Are they the best tools for fighting asymmetrical warfare today against guerrilla forces and armed tribes?

Then there is the commitment to two vast new aircraft carriers costing so much that they have swallowed up nearly all of the Royal Navy budget for years ahead. Surely a modern navy needs lots of small, fast and flexible vessels, not hulking giant floating airports.

There is also the question of nuclear deterrence. Most accept that the U.K. should stay in the nuclear club, if only to hold an important bargaining chip in the global nuclear proliferation debate and to provide basic insurance against any rogue states that might threaten the country. Does that mean sticking to current, vastly expensive plans to upgrade the whole Trident missile system? And to build, over the next decade or so, a fleet of immense new submarines to carry the new nuclear weapons — which anyway depend heavily on U.S. technology and supply?

Why, ask well-informed critics, does the U.K. not limit itself to a cheaper deterrent, using smaller submarines and existing missile technology? Admittedly this might limit the range of nuclear deterrent weapons, which might not even be able to reach as far as Moscow. Isn't Moscow today supposed to be a friend?

Behind these questions lie fundamental shifts in thinking about the future role of armies, navies and air forces.

What cannot be denied is that the global information revolution involves a huge shift in the nature, speed, predictability and intensity of attacks on a country. Microchips and other advances in technology alter the whole balance. Smaller — and often cheaper and easily procurable — weapons can be just as effective.

A modern Sun Tzu, author of the famous "The Art of War," might therefore offer these sort of thoughts on the future conduct of warfare and conflict:

1. The right response has to mean organizing, training and equipping armed forces (air, sea and land-based) in new ways. Military experts always say they need many years to design, plan and procure equipment. But they may be thinking the wrong way and ordering the wrong equipment. Modern defense and security cannot be built around ponderous — and massively expensive — long-term equipment processes. By the time they are ready, they will have long become out of date and useless.

2. The new conflict context points to major emphasis on manpower and human-scale equipment. Of course, some heavy and clever weapons are part of the story, but an even bigger part is having enough personnel on the ground with really good individual communications links and small high-tech weaponry, bomb detectors, counterguerrilla techniques etc.

3. Cyber warfare and techniques for knocking out electronic communications are going to be part of the story. Generally, national defense forces today must be equally prepared for warfare from within and warfare from behind. It is the surprise enemy within that may be of greatest danger.

4. It may be the that the greatest need is for very high quality manpower — officers trained to innovate, improvise, understand locals and, above all, respect other cultures, history and customs.

5. Perhaps defense spending should be viewed in the wider security context of overall national domestic security and intelligence, soft-power projection around the world and top-class contributions to international institutions (maybe new ones) and alliances.

6. The best military forces can only operate within a clear envelope of national priorities, mission and purposes. If the politicians cannot define clearly what national priorities are, then the military will have an impossible task. That may be the most fundamental problem for the military of all.