It is a truism, but, when war is declared, truth is the first casualty, as US Senator Hiram Johnson remarked in 1917. Nevertheless, instilling belief in the cause is vital if people are going to be persuaded to support military action.
The task in this war on terrorism is a particularly complex one: not only do people at home need persuading, but so do the people of Afghanistan, and the Middle East. It takes words, film, newspaper headlines, radio broadcasts, and food drops. It requires demonising the enemy, spinning the truth, censoring information, and making heroes of our forces.
Yet on one front the propaganda war is being won, easily. Downing Street and the military chiefs have never had it so good. Almost the only information the press has to go on is supplied directly from the allied commanders. We are told what they want us to know. This is the first conflict in the age of satellite TV pictures where no reporter has been present to witness the bombing.
Instead many journalists are relying on the government line: data processed by Glasgow University's media monitoring unit indicates a marked tendency for the early evening news bulletins to follow the agenda set by Mr Blair and Mr Bush, with a wider range of views evident on programmes such as Newsnight.
The generals love it. There is no one to check the veracity of allied briefings, of claims of successful hits against military installations. What journalists there are on the ground work for the Qatar-based Al-Jazeera television station, and Whitehall has been doing its utmost in private briefings to rubbish Al-Jazeera as being naturally biased towards the Taliban/Osama bin Laden cause.
The first night of attacks involved 15 bombers, 25 strike aircraft and 50 sea-launched Tomahawk cruise missiles. At the following day's briefing the press was told that 85 per cent of the "ordnance" ( a word beloved of militarists) had hit their targets successfully. What happened to the other 15 per cent? Assuming that each bomber dropped one bomb and each aircraft fired one missile that would make more than 13 bombs and missiles that did not reach their intended destination. Where did they go? Assume that 13 bombs and missiles hit Britain during the night: what sort of story would that make? But there is just silence.
At times like this, Whitehall, the military and much of the media become locked in a collective vice-like grip of "need to know" patriotism. Even to ask such questions, illicits a sneer .
Anyone who probes too hard, who refuses to swallow the daily spoonfeeding, is seen as being anti-British. So it is that we are shown "before and after" pictures of what we are informed is a Bin Laden training camp, even though Mr bin Laden's camps have almost certainly been empty for ages.
In the vast military complex that is the Fort Bragg US Army base in North Carolina, one group of soldiers stands apart. While their colleagues rehearse helicopter landings and machine-gun assaults, this lot discuss font types and weights of paper. They are members of 4th Psychological Operations Group; motto: "Persuade, Change and Influence." They deluge the Afghan people with leaflets exhorting them to reject the Taliban and Osama bin Laden.
Meanwhile, Voice of America is broadcasting to the region, infuriating Taliban leaders who object to reports delivered in Pashto, listing the options open to them. Now they are having to withstand their people receiving coalition accounts of the missile attacks.
But hitting waverers in Afghanistan is just one aspect of the propaganda war. The rest of the Muslim world is also being targeted, with claims that this is not an assault on their religion and constant efforts to portray Mr bin Laden as mad, isolated and self-serving. This front, admit Whitehall sources, is not going so well. While it was a PR coup having Tony Blair on Al-Jazeera, which previously carried Mr bin Laden's post-bombing call to arms, it had little effect. The interview was tougher than expected and Mr Blair's performance was not his most assured.
Even that did not matter so much as the sheer immovability of much of his Muslim audience. "Their minds are made up, this is a war against Islam and little will change that," said one source. "For years they have learnt to mistrust their own leaders, so why should they believe them and their friends now?"
The war planners know the press would prefer to fill space with eye-witness accounts from the ground. But we do not have anyone there. Kabul has chosen not to follow Baghdad and Belgrade and to invite the cameras in. From Whitehall there is a huge sigh of "Thank God". In those wars, they were struggling to catch up. They bombed an air-raid shelter in Baghdad. Horrific. They devastated the Chinese embassy in Belgrade. Terrible. Not this time. Now they show us what their "ordnance" has done – not the other way round. We are given crumbs. By now, hundreds of bombs and missiles have smashed into Afghanistan, but all we are given is pictures of the consequences of just a few. Of the rest, not a glimpse.
When trainee officers attend their courses they spend hour upon hour studying earlier wars and campaigns. They learn from the mistakes and successes of others. They know, to quote Marshall McLuhan, that "Vietnam was lost in the living-rooms of America, not the battlefields of Vietnam". They are not going to make that mistake in Afghanistan.