The LRSO Nuclear Cruise Missile and Tailored Deterrence

As stated in my previous post there were two big strategic nuclear news items this week, one Kim Jong Un’s visit to the Chemical Material Institute of the Academy of Defence Sciences, and the other the US Air Force’s awarding of $900 million contracts to Lockheed Martin and Raytheon to develop competing designs and prototypes for the Long Range Standoff nuclear cruise missile by 2022.

The US Air Force wants 1,000 to 1,100 LRSO cruise missiles. Not all of them will be nuclear armed.

The first news item, the Kim visit, attracted more attention, because nuclear weapons pointing toward the United States grabs more headlines than nuclear weapons pointing from the United States. In my previous post I towed the party line and discussed the first, now I would like to discuss the second.

The LRSO is to replace the AGM-86B cruise missile deployed on the B-52H bomber, and one important effect of the LRSO will be the keeping of the B-52 in the nuclear game. The LRSO, like the AGM-86B, will feature the W80 warhead a topic to which I shall return.

The LRSO will be deployed on the B-52H, the B2-A stealth bomber and the projected B-21 Raider strategic bomber. The B-21 forms an important part of US nuclear modernisation programmes. This will mean that the B2-A and the B-21 will be deployed with both the B61-12 (the major B61 LEP modification) and the LRSO.

There are a number of improvements that the Air Force would like the LRSO to possesses over the AGM-86B, those focused on here are (a) stealth (b) retargeting and (c) variable yield.

Stealth forms one of the most important public selling points of the LRSO. According to the US Air Force the LRSO is necessary because advancing integrated air defence systems, such as the Russian S-400 and S-500, make the AGM-86B vulnerable to surface to air missile fire and so to ensure the continued viability of their mission set a new, stealthier, stand-off nuclear cruise missile is needed.

Now retargeting, a potential new capability for the LRSO, is most interesting. The AGM-86B relies upon inertial navigation and terrain contour matching, key to modern cruise missile capabilities, however the LRSO may well have the capability of receiving and transmitting information in which case it can be retargeted whilst in flight. In flight retargeting is one of the essential new features of the post cold war strategic war planning system, which has moved on from the old Single Integrated Operational Plan concept of operations.

The AGM-86B uses the W80 warhead which can have yields of 5 and 150 Kt. The 5 Kt yield doubtless is reflective of a nuclear explosive yield caused by nuclear reactions exclusively in the fissile primary, whereas the 150 Kt yield is doubtless associated with an explosive nuclear yield caused by nuclear reactions in both the fissile and thermonuclear stages. That’s a variable yield but it is not necessarily a dial-a-yield option where there exists greater range and selectivity. The W80 warhead is being modernised as part of the LEP programme, and it may well be modified to have a dial-a-yield capability including perhaps a yield option less than 5 Kt, which is militarily doable given that the LRSO will also have enhanced accuracy.

Those three potential LRSO capabilities are important from the perspective of “tailored deterrence,” which is the idea that nuclear weapons need to be tailored to multiple mission sets rather than devoted to one exclusive mission type and mission only, say hitting a specific hardened ICBM silo. Tailored deterrence, which relaxes the rationality criterion of traditional deterrence theory, was a core concept that underpinned the Bush era Nuclear Posture Review and it is a key part of the terms of reference of the Trump Nuclear Posture Review, now underway.

B-2A and B21 bombers armed with B61-12 LEP modified warheads and the dial-a-yield W80 stealthy LRSO makes the bomber arm of the strategic triad fit neatly into the tailored deterrence strategic concept. The bomber wing would provide flexibility, all azimuth attack, stealth, earth penetration and in-flight relocation with multiple yield options.

My own view is that tailored deterrence is a new label for an old idea, namely escalation control and intra-war deterrence. The LRSO, and the LEP modifications to the B61, which give it an earth penetrating capacity, are designed to give strategic planners the ability to flexibly tailor strike options during a contingency with the view of controlling escalation.

During the cold war the escalation ladder was accompanied by a plethora of weapon types, but dial-a-yield, retargeting among other innovations fills up the escalation ladder not just with fewer nuclear weapons but with far fewer weapon types. That was one of the main goals of the Bush era Reliable Replacement Warhead, in my opinion.

Critics have, however, rightly pointed out that the LRSO isn’t needed because there are other, conventional, cruise missiles such as the JASSM-ER that can hit similar targets to those envisaged for the LRSO. Hence, the LRSO does not arise from a required military need but is more reflective of the material and institutional needs and concerns of the nuclear weapons complex and the US Air Force.

Furthermore, it is argued that, given that the LRSO will also feature conventional high explosive chemical warheads, in a crisis an accidental nuclear war becomes possible as enemy sensors will not be able to discriminate conventional from nuclear cruise missiles. On top of this we might add the consideration discussed above, which if accurate makes escalation across the nuclear threshold more thinkable and doable.

In sum, it seems to me that the LRSO serves as a good example of how tailored deterrence is used to support claims made for weapons modernisation that has little to do with strategic need, and which has the effect of lowering nuclear security rather than enhancing it.