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Allan Mallinson is a former soldier, and a novelist and writer. His The Making of the British Army is published by Penguin Random House.

Ben Wallace wrote on this site last week that Vladiir Putin should be in no doubt that escalation will meet a robust response. A day earlier, Garvan Walshe described the need for “escalation dominance”.

They’re right, of course. And unthinkable though it may seem, we need therefore to talk about tactical nuclear weapons. We’ve almost forgotten what they were.

The only thing that ever bothered me in the 1980s, when the Cold War was at a dangerous fork in the road and I was commanding a squadron in Germany, was the periodic guard duty at the nuclear ammunition storage site near Paderborn.

It wasn’t the thought of a nuclear accident – where else to be in that event but at ground zero? – or attack by Spetsnaz or terrorist gangs, for we could have dealt with that. Rather was it the military police battalion of the 59th (US) Ordnance Brigade (Special Ammunition Support).

The MPs’ job was security, and they took it hyper-seriously. (If not, why not?). A Lance Corporal that stumbled when interrogated about his precise orders could bring a career-stopping rebuke from the Commander-in-Chief for the officer in command.

The ammunition was nothing to do with the strategic nuclear deterrent (Polaris), technically. These were low-yield shells for the Royal Artillery’s eight-inch calibre howitzer (range about 12 miles), and warheads for the Lance ballistic missile (range, 50 miles or so): they were tactical – “battlefield” – nuclear weapons (TNW).

Each national contingent on NATO’s Central Front — the US, British, Canadian, German, Dutch and Belgian — fielded the same delivery systems, but the warheads were American, to be out-loaded during a crisis, and fiercely guarded for the rest of the time.

The Royal Air Force (Germany), along with the other national air contingents, had sub-strategic nuclear bombs and missiles of their own. The targets of RAF(G)’s TNWs were troop concentrations to the east of the River Weser, in the event of Soviet spearheads breaching the so-called Weser Line on the western side of the Upper Weser valley. The Lances and howitzers of the Royal Artillery’s 39th Heavy and 50th Missile regiments would have joined in the interdiction.

That, however, was the purely military view of TNW, and there were indeed some who regarded nuclear artillery as “just a bigger bang.”

The other view was that of the policy staff in Whitehall. I remember during my first week in the directorate of military operations being told by a senior mandarin that the General Staff did not understand deterrence.

In essence, the policy staff’s view was that of Sir Humphrey Appleby when he explained Deterrence to the Jim Hacker in Yes, Prime Minister.  Hacker thought he probably wouldn’t use Trident in the event of a nuclear attack on Britain, and that they, the Soviets, probably knew it – so buying Trident was pointless.

Sir Humphrey agreed, up to a point: “Yes, they probably know that you probably wouldn’t. But they can’t certainly know.”

Hacker doubted this. “They probably certainly know that I probably wouldn’t.”

Sir Humphrey was then at pains to explain the essential element of uncertainty in deterrence theory: “Yes, but though they probably certainly know that you probably wouldn’t, they don’t certainly know that, although you probably wouldn’t, there is no probability that you certainly would.”

Which is why when in 2015 Jeremy Corbyn, pressed by Sarah Montague, the Today presenter, on whether there were any circumstances in which he would use the nuclear option, said “No”, he effectively cancelled deterrence and made himself unelectable as Prime Minister.

Sir Humphrey didn’t explain to Jim Hacker the role of TNW in deterrence theory. It was comedy, after all, and the joke was better delivered quickly. But the purpose of TNW, said the real Sir Humphreys in the 1980s, was to provide a plausible ladder of escalation: graduated response, rather than the erstwhile and rather less plausible doctrine of massive retaliation, with its notion of mutually assured destruction.

What those eight-inch nuclear shells did was provide multiple threads in the seamless cloak of escalatory deterrence logic – from the first rifle shots as Soviet troops set foot across the Inner German Border, to the release of multiple warheads over Russian cities.

TNWs weren’t meant to be used; they were meant to demonstrate that the cloak of deterrence was indeed seamless, and that there was therefore real peril for the Soviets in any offensive. Strategic and tactical nuclear weapons were inseparable in deterring both conventional and nuclear attack, which was why NATO could never sign up to “no first use.”

The Soviets had to be convinced of the real peril, of course – and so the soldiers and airmen had to plan for the actual use of TNW, practise their firing, and store the warheads and missiles well forward. And indeed the policy staff tended to view calls for any substantial strengthening of conventional defence, as the soldiers were always urging, as potentially diminishing deterrence, since it might increase the threshold of tactical nuclear release and therefore tempt a Soviet conventional attack with limited objectives.

Some soldiers thought this was all nonsense. Several chiefs of the general staff in the 1980s, notably two of the most cerebral – Dwin Bramall and Nigel Bagnall – would happily have scrapped all nuclear weapons, strategic and tactical.

They supposed the Soviets acted with the same rationality as they themselves, and were probably right to, although we’ll never know because the Soviet leadership was never put to the ultimate test. The arguments ceased with the collapse of the Soviet Union, when TNW were withdrawn from Europe and, in effect, scrapped. The Russians, on the other hand, did not scrap theirs.

Putin quite evidently acts with a different rationality, his logic based on different premises. What if, therefore, in contemplating using TNW, he becomes sufficiently certain that NATO, unable to respond with other than strategic nuclear weapons, will never gain the authority of its members to escalate?

In the public imagination, his crude but tellingly vague nuclear threats over Ukraine suggest intercontinental strikes. But what if he were contemplating a TNW strike against a “legitimate military target”? And how, in any future confrontation with NATO, would the alliance deter that same threat — or if deterrence fails, would restore deterrence?

To win Cold War Two, we must get real again about deterrence. NATO rearmament must address the seam that has been inserted in the previously seamless cloak.