LAURENCE REES: To what extent in 1940 was Britain genuinely at risk of defeat?

RICHARD OVERY: There’s a popular argument now that Hitler never really intended to invade Britain and that the Battle of Britain was in some sense an unnecessary battle. Quite a bit of historical writing has suggested this argument. I think this is nonsense. Hitler’s plans to invade Britain are, of course, rather half-hearted, and it’s an extremely difficult operation to carry out. But if Hitler could have got a cheap victory in 1940 it would have absolutely suited him. It would have created the conditions which make possible the great drive to the East and so on, it would probably keep the United States out of any involvement in the war and it would have created, I think, a geopolitical position for Hitler which would have been entirely satisfactory.

The Germans have massive air power and they massively underrated the capacity of the RAF to withstand attacks. I think if Hitler had been able to get his cheap victory in the autumn by pounding British cities and so on and killed, well, he kills 40,000 people. This had never happened before in war, numbers haven’t been killed like that at any point in the First World War. It’s a huge impact and I think that he did convince himself that by destroying the RAF and being able to bomb British cities you would create the circumstances in which either the British would give up or you could have a cheap invasion. He didn’t rate the British Army at all and the British Army’s ability to withstand half a dozen German divisions in 1940 was extremely limited. But of course that doesn’t happen and as we focus more and more on the war to the East and the planning that goes on from August 1940 onwards it’s tempting to say that it was always a side-show. But I think he was serious about it.

If he could have picked up a cheap victory, transporting his divisions across to Kent and Sussex with British air power effectively neutralized, then the Royal Navy, which people sometimes say would have been the barrier, would have suffered exactly the same way that the Prince of Wales suffered when it arrived in the Far East; it would have been sunk by German dive bombers. Because you had to imagine the fleet coming down now with the RAF neutralised; so there’s no air help coming over from the RAF. I think the Royal Navy would have faced enormous difficulties if German air power was focused entirely on the invasion area. So I think we dismiss Sealion in Britain too readily and as a result fail to recognise how important the strategic and tactical decisions taken surrounding the Battle of Britain actually were. Though we didn’t win it exactly, it’s an important battle to undertake.

LAURENCE REES: But many people I’ve talked to say that they Germans didn't have the capacity to mount an invasion in 1940, even if the Battle of Britain had gone differently…

RICHARD OVERY: No, it’s not inconceivable. It depends very much on changing circumstances. You have to imagine the RAF defeated. You have to imagine that German air power can roam freely over the whole of Southern England by day. You have to imagine that they gather together the necessary shipping, and what they’re moving across are half a dozen battle hardened, heavily armoured divisions and they’re facing an army that’s retreated in poor order and is desperately trying to find tanks and guns again. This army has very little training and is certainly anything but battle hardened. In fact 50,000 of those battle hardened troops end up in German POW camps. It’s not inconceivable that he could have undertaken that.

You’ve got to think, for example, of what happened in Crete. An extremely difficult operation for the Germans: they’re outnumbered when they arrive in Crete, and British commanders and the British Commonwealth soldiers make a pig’s ear of it. Now you have to imagine that on a larger scale in Southern England, and I think that with all the best will in the world it’s difficult to imagine that as those German divisions are reinforced and reinforced, they’re not able to achieve a good deal. Look at Norway. In that case the Germans win despite the circumstances. But it wasn’t possible in Britain because the Luftwaffe was simply not up to winning air superiority over British soil.

LAURENCE REES: So you think that the most crucial battle of the war was the Battle of Britain?

RICHARD OVERY: I think the Battle of Britain is a very important battle, and understanding that that was what Britain needed to do is one of the few things that Chamberlain does in the 1930s that people have not bothered to explore too much. But Chamberlain, when he reads the assessments, recognises what matters strategically, and throws his weight behind expanding fighter command and building the radar chain, making sure that if the worst happens we can at least defend ourselves, and that was a very important decision. This was a different decision from somebody like Churchill who was saying that what we need is to beef up the French Army and have lots of aircraft we can send to France and so on. He didn’t understand all this radar stuff, which would mean that you would end up in a situation where the Luftwaffe would indeed be able to establish air superiority.

So of all the priorities the British have in the 1930s this is the one they put at the forefront. And it is a very important one because you’ve got to be able to defend Britain under the new circumstances of air warfare and mobile warfare, as if you can’t do that Southern Britain is very vulnerable.

LAURENCE REES: So we owe Neville Chamberlain a huge amount?

RICHARD OVERY: We owe Chamberlain more than people normally allow him. He doesn’t have Churchill’s flamboyance as a war leader or as a potential war leader but he’s a shrewd man and he weighed up what Britain’s priorities were and what we needed to be able to do. He also strengthened the Navy too. The Navy and air power was what Britain was good at. Fighting on land was what we were not good at, and never really became very good at throughout the war.