God presents a particular problem in our current struggles with violent Islam. The job I'd like least is probably that of an armed forces chaplain. Some of his job is perennial: allaying anxieties among young men and women far from home, or dealing with grief over the loss of a comrade from within the closely knit units, which the memoirs of veterans of earlier conflicts such as George MacDonald Fraser have made so vivid. 

The status of religion within these campaigns is made difficult by the fact that our opponents go into battle shouting "Allahu akbar" ("Allah is Great"), while our own forces' ranks include soldiers who are Muslims as well as Christians, and people of other faiths or none. One in 400 men serving in the US armed forces is a Muslim. The medieval crusaders' cry of "Deus le veult" is obviously out of kilter with armies which are officially secular, as President George W. Bush discovered when he unfortunately used the word "crusade" in this context. Claiming that "we are fighting for Western civilisation" is difficult, since there are several other civilisations, from communist China via Hindu India to Muslim Indonesia, which are similarly engaged in fighting Islamist terrorism. The concept probably does not have much local purchase either among Protestant fundamentalists who regard much of our own civilisation as the work of the Devil. A large number of US military chaplains are drawn from this evangelical background.

If one concludes that God is too contentious in our present expeditionary travails, except as solace for individuals, then it is all the more important that we are clear in our own minds about the moral contest we are engaged in. We are rightly asked to admire the bravery of our young soldiers and airmen. 

But this conflict is not just about them, but also the organised will of civilian and secularised societies to sustain a struggle, not for four, five or nine years, but perhaps 50, often in the face of doubting or fashionable opinion. 

That is part of the military covenant too, along with boots, housing, rifles and armoured vehicles. The enemy is protean and may well strike from Somalia, Yemen, Mali or Mauritania by way of people who live in Bradford, Luton or Walthamstow as our fellow citizens. 

The moral universe (such as it is) of our opponents — one is tempted to say their moralised hysteria — is not a subject we are handling very well. Indeed, I am tempted to say that Liddell Hart's equation of Nazism with bad manners anticipates many of our current problems in explaining why we are at war, for manners often include a reluctance to give offence, which I have endeavoured to avoid.