Air University Review, November-December 1982

Throw-Weight and Arms Control

The United States and the Soviet Union commenced Strategic Arms Reduction Talks (START) in the summer of 1982.

Achieving a reduction in strategic nuclear weapons will require both parties to negotiate throw-weight as either an overall unit of limitation or as part of a comprehensive package.

Throw-weight was defined in the 1979 SALT II agreements as being the sum of the weight of a missile’s reentry vehicles (RVs), self-contained dispensing mechanisms, and penetration aids.¹ Although the bulk of throw-weight comes from the payload, or the warhead, the term is not interchangeable. Throw-weight is more than just the payload.

ICBM Throw-Weight in SALT II

The term itself was used throughout the Treaty and other accompanying documents because it was a unit of measurement which attempted to define classes of missiles and launchers as well as certain characteristics of missiles themselves. For example, to define a "heavy" ICBM, one of the SALT II criteria was any missile which has a throw-weight exceeding that of the current heaviest light ICBM. The United States then stated that this was the Soviet SS-19.² In promulgating this definition, the United States made a major concession to the Soviet Union since the previous SALT I definition of a heavy was a missile with a significantly lesser throw-weight.

Using this throw-weight boundary between heavy and light ICBMs, each party was then restricted to developing only one light ICBM during the period of the Treaty. The United States was thereby denied equality in one major classification of missile, building new heavy ICBMs to replace the aging Titan.

Throw-weight was also used to demonstrate that a new type of missile had been developed. Variations of over 5 percent in throw-weight constituted prima facie evidence that a new type had in fact been developed. Variations of only 10 percent of throw-weight in test missiles were allowable in order to ensure that only one missile type was being developed in a series. In an effort to prevent MIRVing of currently single RV-capable ICBMs, individual RV weights were not to be less than 50 percent of the throw-weight of existing ICBM launchers. In both cases the maximum throw-weight of each class missile or launcher would be that of the Soviets SS-19.

In their effort to gain support for SALT II, Carter administration spokesmen inferred that the Treaty limited throw-weight. This is not completely true. Although throw-weight was used throughout the Treaty and accompanying documents, no effort was made to use throw-weight as a unit of limitation for numbers of missiles. By limiting launchers, the illusion of an arms control agreement was obtained, but in fact the Soviet Union was unrestrained from building an unlimited number of missiles with which to reload reusable missile launchers. This unlimited missile stockpiling could have been restrained by setting an aggregate throw-weight ceiling. An overall ceiling, individual subceilings, or some combination could have been used to limit the missiles themselves.

The Soviets circumvented SALT II at the time of the signing when they failed to list the SS-20 as an ICBM. The SS-20 was claimed to have less than a 5500 kilometer range; hence it was not SALT II accountable. Yet by lessening the payload, ranges of up to 7400 kilometers are possible.³

Throw-weight could have been specified to limit individual missiles such as the SS-20. The tested throw-weight would have had to be known as would the test payload. Variations of alternate payloads would have to be considered in order to classify the missile properly as an ICBM or otherwise. Some missiles might fall into an unclear category. Failure to include individual missile throw-weight limitations in SALT II allowed the Soviets to develop an unlimited number of SS-20 missiles, which probably should have been considered an ICBM.

Impact of SALT Failure
to Control ICBM Throw-Weight

One of the key failures of SALT I was its inability to control either aggregate or individual throw-weight. Although not part of the SALT I treaties, the definition of a heavy ICBM was clearly identified by the United States as any that significantly exceeds the volume of the heaviest light ICBM of the time. This was the Soviet SS-11. By using this volume unit of limitation, instead of throw-weight, the Soviets were able to circumvent the intent of the SALT I Treaty. Their next generation of ICBMs (SS-17 and SS-19) exceeded SS-11 missile volume, but due to cold launch, launcher volume was the same.⁴

Advances in individual missile throw-weight, increased accuracies, higher yields, and MIRV are direct causes for the first strike counterforce threat to U.S. ICBM silos. The growth of Soviet ICBM throw-weight (in pounds) from the period of SALT I to SALT II was as follows: 6,845,500 (1972); 9,163,750 (1979); and 9,859,625 (1981).⁵

Total Soviet throw-weight grew by 44 percent from the time of SALT I until 1981. The circumvention of SALT I volume limitations allowed the Soviet SS-18 to have a 38 percent greater throw-weight than the SS-9, the earlier Soviet "heavy." Although the SS-11 was supposed to be the upper limit for "light" ICBMs, the Soviets built the SS-17 and SS-l9 which have up to 400 percent greater individual throw-weight than the SS-11. They then convinced the United States to redefine "heavy" so that these missiles were not considered "light." A direct comparison of U.S. ICBM throw-weight (in pounds) during the same period is 1,855,675 (1972); 1,979,050 (1979); and 1,963,275 (1981).

Despite Public Law 92-448, which states that arms control agreements subsequent to SALT I must codify equality, it can be seen that the Soviets 3.6 to 1 advantage in throw-weight at the time of SALT I increased to 4.6 to 1 by the time of SALT II and is 5 to 1 today. U.S. throw-weight grew a total of only 7 percent between the two treaties and has actually decreased since 1979.

A further failure of SALT I to constrain growth and military capability of strategic arms can be seen by a comparison of MIRV-capable ICBM throw-weight. The U.S.S.R. had none in 1971 and 5,877,050 pounds in 1979; whereas the U.S. had 414,750 pounds in 1972 and 1,086,250 pounds in 1979. This comparison demonstrates a shift from U.S. domination of the field to a 5.4 to 1 Soviet advantage in 1979.

The growth of Soviet military capability during this period of SALT and détente can also be measured by comparing the destructive power of the ICBM force. One such unit of measurement is equivalent megatonnage (EMT). EMT, calculated by raw megatonnage 2/3 x number of RVs, gives the analyst some idea of barrage capability or soft-target kill potential. It is useful in determining the possibility of destruction of mobile military targets but not necessarily hardened silos.

EMT increases are directly related to increasing raw yield, which increases with throw-weight. Since it takes roughly eight times the raw yield to double the destructive blast damage from a nuclear device, EMT growth does not directly parallel throw-weight growth. For example, EMT (in million tons) was 4259 in 1972 and 5284.5 in 1979 for the U.S.S.R. and 1360 in 1972 and 1312 in 1979 for the U.S. during the era of détente. Soviet growth was 24 percent while the United States showed a 3 percent net decline in capability. In 1979 the Soviets enjoyed a 4 to 1 advantage in EMT.

SALT, Throw-Weight, and SLBMs

Launchers were also used as the unit of limitation for SLBMs in SALT I. By failing to control individual missile throw-weight, the Soviet Union significantly upgraded its naval strategic nuclear force. Missiles were developed that had greater throw-weight, higher yields, and MIRVing.

In SALT II, development of SLBMs was limited by placing a ceiling on individual missile throw-weight. As with light ICBMs, the upper limit for new SLBMs was the throw-weight of the SS-l9. This really was no limit since the SS-l9 throw-weight (over 7000 pounds) greatly exceeded any SLBM under development. The growth in SLBM throw-weight in pounds for the U.S.S.R. was 624,000 (1972); 1,868,000 (1979); 2,112,000 (1981); and for the U.S. 848,000 (1972); 1,168,000 (1979); and 1,160,000 (1981).⁶ Again, a pattern of Soviet advantage appears (1.8 to 1 today, despite a U.S. lead in 1972). Soviet SLBM throw-weight grew 238 percent since SALT I while the corresponding U.S. growth was only 37 percent. A comparison was made for SLBM equivalent megatonnage. At the time of SALT I, the U.S. had an advantage in SLBM EMT. The growth in SLBM equivalent megatonnage (EMT in millions of tons) for the U.S.S.R. was 531 (1972), 1384.5 (1979), 1505 (1981); for the U.S. a total of 574 (1972), 703 (1979), and 675 (1981). Again, there is a current 2.2 to 1 advantage in SLBM EMT for the Soviet Union as well. Soviet EMT grew 183 percent while the U.S. only 18 percent.

There are some problems when using SLBM throw-weight for arms control purposes. As with all missiles, riot all of the force will be operationally ready due to scheduled and unscheduled maintenance and other circumstances. Not all of the SSBN force is on patrol at any one time.

For example, it is reported that the Soviets can keep only 10 to 15 percent of their Yankee class submarines on patrol at any one time. Perhaps this is the maximum number that can be routinely sustained.⁷

Polaris/Poseidon hulls are on station roughly 55 percent of the time. Ohio class submarine availability is projected to be 66 percent. Without knowledge of actual Soviet patrol patterns, it is impossible to ascertain if their advantages in SLBM throw-weight are offset by advantages in U.S. sustainability.

It is also important to note that in the SLBM field there are a number of uncertainties which make speculation difficult. Identification of classes of submarines, numbers of launchers on each type unit, and types of missiles in each launcher is by no means certain. Few unclassified sources agree on the correct number of Golf and Hotel class modifications nor on how many launchers are on each. Then, too, there is the possibility that some SLBMs are assigned for naval targets at sea.⁸ On the other hand, Golf and Hotel submarines assigned theater missions can suddenly become strategic if the Soviets utilize submarine support facilities in the Caribbean. In short, the SLBM question is not as neat as the ICBM.

Flexibility and Throw-Weight

Advantages in throw-weight can bring increased flexibility. As throw-weight grows, capabilities increase, including MIRV, longer ranges, and counterforce. The Soviets’ SLBM SS-N-l8 illustrates these points. Their single RV version (Mod 2) can travel the farthest (4320 nautical miles). Keeping the volume of the missile and launcher the same, payload may be altered allowing for MIRV, the price being a shorter range (3510 nautical miles). Thus the SS-N-l8 allows for more targeting flexibility than its predecessor, the SS-N-8.

Interestingly enough, the height of the SS-N-18 appears only to be 1 meter or so greater than the SS-N-8. This may mean that advances in fuel were achieved, which also impacts on arms control. Throw-weight limits might also aid in reducing fuel circumvention of limitations based on volume or size of missiles or launchers.

The U.S. position during past arms control negotiations was to use the maximum observed throw-weight of each missile. For the U.S. Poseidon (C-3) missile, that meant when it was tested with the maximum number of RVs (14). This missile is not reportedly deployed with 14 RVs; hence, the operational throw-weight of a significant part of our SLBM force is actually less than what we calculated it was during negotiations.

Limitations on Use of Throw-Weight

Throw-weight is particularly unsuited for use as a limit for manned bombers, air-launched ballistic missiles (ALBMs), and cruise missiles. There are numerous formulas for converting these into equivalent ICBMs or warheads. Not all aircraft, however, would be airborne, on alert, in their patrol area at any one time.

Then, too, there is the question of bomber/tanker susceptibility to a preemptive attack and bomber/cruise missile penetration of Soviet air defenses. There is also the lack of timeliness. Manned aircraft are not the equivalent of the ICBM in time-urgent hard target kill capability. Rapid retargeting also is a problem which is being worked on. If manned bombers, air-launched ballistic missiles, or cruise missiles are not the equivalent of the ICBM, there should not be any effort made to contrive a method where they might be judged as so, even for purposes of an arms control agreement.

Throw-weight can be determined by using intelligence estimates, attempting to give equivalence using U.S. systems as the base, or by having access to telemetry data during testing. The Soviets have been especially reluctant to grant the latter. A mutually agreed-on data base could also assist in getting throw-weight data. The historical precedents of Soviet failures to agree to the definition of heavy ICBMs in SALT I or to acknowledge the U.S. launch and throw-weights of the SS-19 during SALT II make the prospects for actually obtaining a Soviet data base bleak.

When using throw-weights, it will be necessary to ensure that aggregate amounts are more than just the totals of missiles on launchers. Aggregate must mean total including all stockpiles and reloads. Ref ire on mobile systems and cold launch make this imperative.

It is probable that the Soviets will immediately reject throw-weight as a unit of limitation since they have been successful in remaining essentially unconstrained while using launchers.

Throw-Weight and START

Throw-weight can be useful in limiting ICBMs and SLBMs as long as the problems of SSBN availability and fuel/range circumvention are taken into account. Throw-weight can be used to constrain individual missiles, total numbers of missiles, development of new missiles, and/or further MIRVing of existing missiles.

Individual missile throw-weight can be used to prevent upgrading payload capability due to fuel advances. A parallel range limitation would also be required in order not to transfer changes in throw-weight or fuel to range. Throw-weight of missiles in the grey area between ICBM and some shorter range also needs to be identified to prevent circumvention of development of ICBMs tested at shorter ranges or with varying payloads.

Individual missile throw-weight can be used to constrain further MIRVing of some of the Soviet Navy and Strategic Rocket Force missiles which still have one RV. This could be done as was outlined in SALT II by requiring RV weights to be more than 50 percent of an individual missile’s throw-weight. START MIRV limitations should not restrain Minuteman upgrading. SALT II attempted to restrict numbers and types of new missiles by tolerances in throw-weight during testing. This method could probably be used in START.

Aggregate throw-weight can be used as a simple method of total missile limitation or limitations on classes of missiles. This would allow each side to mix types of missiles within each class or classes within an overall ceiling. In an effort to ensure simplicity, restrictions on MIRVing itself could be avoided. Using an aggregate ceiling has its pitfalls, however, since if not cut deep enough, no real reduction in military capability of the Soviet Union would occur. Total Soviet and U.S. throw-weight and corresponding equivalent megatonnage at the end of 1981 can be listed as follows:

Aggregate ICBM/SLBM Capability

Reductions in strategic arms will require redressing the total 4 to 1 Soviet advantage in throw-weight and their 3.5 to 1 advantage in EMT. These current advantages have allowed the Soviets to build a first-strike counterforce military machine. Throw-weight limitations can be used to reduce this threat.

Limitations might be attempted by having the Soviets de-MIRV the SS-l8 missile, using individual throw-weight as the criterion. If the SS-l8 had only one warhead per missile and aggregate subceilings limited missiles, then U.S. ICBM vulnerability might be reduced. DeMIRVing the SS-N-l8 and the new SS-N-20 might also be possible.

Throw-weight limitations must not be allowed to constrain the need for the United States to upgrade its force to some reduced but equal Soviet ceiling. Force levels and a national strategy will need to be decided on first. Negotiating positions should come later. The clear Soviet advantage in the military utility of their missile forces has come in part due to previous failures to constrain throw-weight.

Throw-weight advantages allow improved dispensing mechanisms. Similarly, higher throw-weight allows the option of carrying electronic warfare and other penetration aids that impact on plans for active defenses. Higher throw-weights also allow hardening missiles against electromagnetic pulse (EMP) without having to make significant range or payload compromises. Throw-weight advantages have allowed the Soviet Union to reduce the uncertainties they face due to the inability to predict accuracies in operational missions. Higher yields mean that greater inaccuracies can be accepted in order to achieve the same level of destruction against hard targets. This flexibility is not shared by the United States.

Negotiators in START must understand these technical aspects if there is to be a meaningful arms reduction agreement. Finding an effective and enforceable compliance policy will be difficult and in part depend on adequate verification. Throw-weight will not be easy to verify, but then, again, the purpose of an agreement is not verification but rather deterrence and stability. An arms control agreement which at least attempts to restrain throw-weight is more likely to have some meaningful measure of effectiveness than the present lack of any restraints.

1. Second Agreed Statement to paragraph 7 of Article II of the SALT II Treaty. It is recognized that there is a significant legal distinction between the Treaty and these Agreed Statements. Since the Treaty is not in force legally and the SALT II concept was sold as a package using these statements and understandings, no distinction will be made in this article.

2. The United States made a unilateral" statement regarding the method of defining "heavy" ICBMs similar to what was done during SALT I. On 16 August 1977, the United States informed the Soviet Union that they considered the upper throw-weight limitation for a light ICBM to be 3600 kilograms (approximately 7936 pounds). The Soviets did not respond. See Secretary of State Cyrus Vance’s statement on page 17 of SALT II Agreement: Vienna June 18, 1979, Selected Documents No. 12B by the Bureau of Public Affairs, U.S. Department of State, July 1979. Throw-weight was not the only unit of limitation used to divide heavies and lights, however. The launch-weight of the SS-19 was also given and not acknowledged. This failure to define basic terms alone should have been grounds to reject the Treaty.

3. SS-20 data taken from the IISS Military Balance 1981-1982, page 105. Mod 2 is the version so often discussed in the European theater, with 3-150 KT RVs. The range of Mod 2 is given at 5600 kilometers. By shifting to a single 50 KT RV, a range of 7400 kilometers is obtained. Both Mods clearly meet the SALT II criterion of being an ICBM, yet the SS-20 is not listed anywhere in the agreed statements or understandings as being a SALT II accountable ICBM. Despite the fact that the Mod I only has a 5000 kilometer range, any missile that has been tested in an ICBM mode is supposed to count.

4. For volume calculations, see Table 19.1 of Dr. Robin Ranger’s Arms & Politics 1958-1978: Arms Control in a Changing Political Context (Toronto: Gage Publishing, 1979), p. 175.

5. The 1972 and 1979 data are taken from John Collins U.S. and Soviet Military Balance: Concept and Capabilities 1960-1980 (New York: McGraw-Hill, 1980), Appendix 2. His breakdown of numbers of varying Mod ICBMs is most useful for 1979. Throw-weight and yields used later were taken from this and the 1978-79 and 1981-82 IISS Military Balance. The lowest and highest given throw-weights were averaged. Data from 1981 were taken from the U.S. Department of Defense Soviet Military Power booklet. These sources are the basis for all subsequent tables.

6. In addition to earlier cited sources, it is necessary to utilize Jane’s Fighting Ships among other sources in order to decide SLBM capabilities. No standardization exists as to Soviet submarine classes. This problem is addressed later. The SS-N-4 and SS-N-20 have been deleted for purposes of this article. SS-N-5 throw-weights were also not calculated since the basic numbers were not available.

7. See the comment by Commander C. C. Holcomb in United States Naval Institute Proceedings, July 1978, pp. 21-22.

8. This subject has been debated recently and is the subject of much speculation. There would be no defense against a ballistic missile aimed at a naval target at sea. See Lieutenant Commander Carl H. Clawson, USN (Ret), "The Wartime Role of Soviet SSBNs-Round Two," in the United States Naval Institute Proceedings, March 1980, pp. 64-71.

Commander James J. Tritten, USN (B.A., American University; M.A., Florida State University), is a student at the U.S. Navy Postgraduate School Detachment, University of Southern California, Los Angeles. As a naval aviator he served in a carrier-based air antisubmarine squadron. Commander Tritten has published articles in military journals, including U.S. Naval Institute Proceedings, Naval War College Review, and Military Review.

The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.

Air & Space Power Home Page | Feedback? Email the Editor