London can take it.

Unlike New Yorkers on 9/11, Londoners on 7/7 — as Thursday's terrorist attacks may come to be known — have been here before. Many times.

The first bombs of the German Blitz fell on central London on Aug. 24, 1940, and there were recurrent waves of aerial attack throughout the war, culminating in the V1 flying bomb and V2 rocket campaigns of 1944 and '45. All told, German air attacks killed around 43,000 British civilians, a large proportion of them Londoners.

Of course, we now know that morale was not uniformly solid during the Blitz. Harold Nicolson, the diarist and member of Parliament, commented acerbically on the loss of nerve suffered by one senior Labor politician during the V2 campaign. Nor was all sweetness and light in the cramped, malodorous Underground stations where Londoners were forced to take shelter. (Yes, the "Tube" knows all about bombing.)

Yet Nicolson himself was rather more typical in his determination to appear (if not to feel) unruffled. "I am nerveless," he noted in his diary after one air raid, "and yet I am conscious that when I hear a motor in the empty streets I tauten myself lest it be a bomb screaming towards me. Underneath, the fibers of one's nerve-resistance must be sapped."

The psychologist Melitta Schmideberg concluded in 1942 that "the majority of the population adapted itself to the new Blitz reality ... by acquiring new standards of safety and danger and by gradually learning to take the bombing as an unpleasant but unavoidable part of life." (This was not, by the way, what pro-appeasement politicians had expected before the war. The conventional wisdom had been that the Luftwaffe would be able to unleash panic and pandemonium within 24 hours of the outbreak of hostilities.)

The British stiff upper lip proved to be a war-winning weapon. Films such as "London Can Take It" — a 10-minute documentary made in the midst of the Blitz in 1940 to document the resilience of British citizens — and the electrifying broadcasts from London by Edward R. Murrow, CBS' bureau chief in London, helped hugely to build American support for Britain. "You burnt the city of London in our homes," wrote the American poet Archibald MacLeish of Murrow's radio broadcasts, "and we felt the flames."

So when I heard the news of Thursday's events, my first thought was that people have bombed London before, and some have lived to regret it.

Having spent much of the week in Berlin — where one can still see the physical scars left by the Allied bombers — I have a rather keen awareness of how we made the Germans pay for the Blitz.

Times change, of course. As I returned to London on Thursday, I was reminded that citizens of the capital today are a lot less buttoned-up than the generation of World War II. They are more easily moved to emotive displays than their grandparents, weeping at the funerals of princesses and — just 24 hours before the terrorists struck — displaying almost embarrassing enthusiasm at the news that their city would host the 2012 Olympics.

But though they may seem softer, today's Londoners have lived through horrifying scenes as well; the Germans were not the last people to bomb London. The Irish Republican Army's mainland bombing campaign is still fresh in the memory of virtually every grown man and woman in the city.

The IRA bombed London in 1973 (two car bombs, one outside the Old Bailey), and again in 1974. In 1982, it killed 11 soldiers in attacks on Hyde and Regents parks. A year later, six people at Harrods. And in 1992, three people outside the Baltic Exchange in the financial district. In 1993, it struck again with a truck bomb at Bishopsgate. And I vividly remember the attack on Docklands in 1996 — because it was immediately outside the office where I was working.

Then, as during the Blitz, the near-universal response could be summed up in the phrase "business as usual." We were all aware that our grandparents had stood much worse without flinching.

To be sure, what happened Thursday was better calculated — and more lethal — than anything the IRA ever managed. Yet once again Londoners have reacted with sang-froid (a French phrase for a very British trait). In any case, we all knew this would happen sooner or later. Since 9/11, I haven't taken the Tube once without asking myself: "Will it be today? Will it be my train?" I have taken it nonetheless. And I shall continue to do so.

No, whoever the perpetrators were, I am confident they will not achieve their aim of disrupting London life. More than that: I am certain they will live — though perhaps not for very long — to regret following in the cloven hoof-prints of the Luftwaffe and their Irish imitators.

London can take it. And dish it out.

Niall Ferguson is a professor of history at Harvard University and a Senior Research Fellow of Jesus College, Oxford.