In a previous post, I projected the number of Aegis BMD ships, and in particular the number of ships with the “advanced” BMD capability, though 2045. I did this primarily because I was interested in the question of how many SM-3 Block IIA interceptors, which have a potentially significant capability to intercept intercontinental-range missiles, are likely to be deployed. In this post, I turn to the question of projecting how many Aegis SM-3 block IIA interceptors the United States might eventually deploy on its ships and at its Aegis Ashore sites.
(1) Projection based on past and planned procurements.
Figure 1 shows the number of SM-3 Block IA, Block IB and Block IIA missiles in inventory based on past procurements and planned future procurements.
Figure 1. Number of SM-3 interceptors in inventory. Diamonds are Block I/IAs, squares are Block IBs, and circles are Block IIAs. Numbers do not include missiles expended in tests or retired because of reaching the end of their service lives.
The numbers in Figure 1 are based on Table 2 of Ronald O’Rourke, “Navy Aegis Ballistic Missile Defense (BMD) Program,” November 10, 2015, and the corresponding tables in earlier versions of this report dating back to 2011. Future deliveries of Block IB and Block IIA missiles beyond 2020 are based on FY 2016 MDA budget documents. Projections beyond 2020 assume an expenditure of one Block IB and one Block IIA per year in tests. Block IA figures for 2009-2010 and Block IB figures for 2011-2013 assume the actual number of interceptors expended in tests in each of those years.
The numbers of Block IA interceptors (and earlier Block I interceptors) are shown by the diamond symbols in Table 1. The spike in the number in FY 2014 is due to an additional order of 23 Block IAs that was placed following delays in the Block IB program. Beyond 2014, the number of Block IAs begins to decline as the missiles reach their service lifetimes of about ten years. It is clear that by the early-to-mid 2020s all of the Block IAs will be out of service.
The blue squares in Figure 1 are for Block IB interceptors. Current plans call for buying a total of 52 Block IBs per year for the next several years. In September 2015, it was reported that the Department of Defense’s planned to buy a total of 396 Block IBs. Figure 1 shows that at the current rate of deliveries, this total number of Block IBs would be reached in 2023 (at that time, the total number of Block IBs delivered is greater than the number in inventory by about 20).
The red circles in Figure 1 show the projected numbers of Block IIA interceptors in inventory through 2023, the last year I could find any data for. Since, as noted in the preceding paragraph, deliveries of the Block IB missiles could end after 2023, additional resources could become available for producing greater numbers of Block IIA interceptors. We can project the number of Block IIA interceptors forward in time by making various assumptions. (All the projections here assume that the Block IIA is not superseded by a more capable missile on time scale considered here.)
As a low estimate, assume that Block IIA deliveries remain at the same rate of 24 per year as currently planned for 2023. This gives a total inventory of about 220 missiles in 2030, assuming a twelve year service life and one missile expended in tests per year. Assuming SM-3 Block IIAs continue in production beyond 2030, the Block IIA equilibrium inventory (in which new deployments are balanced by retirements) will reach a level of about 275 missiles by the mid 2030s. This is shown by the red diamonds in Figure 2 below.
The low estimate above seems highly improbable, as the mid 2030s equilibrium number of Block IIAs is less than half of the number of total number of SM-3 missiles of all types that would be in inventory in 2030. A more reasonable assumption is that total spending on SM-3 missile procurement of all types stays constant. Assuming Block IB deliveries end in 2023, and that a Block IIA interceptors costs twice as much as Block IBs (and not attempting to account for inflation), and using 2022 as the baseline year for the total cost, then the Block IIA inventory would reach about 365 in 2030 with an equilibrium level of about 530 missiles in the mid 2030s. This is shown by the red circles in Figure 2.
A higher equilibrium figure of about 610 Block IIA interceptors, shown with red squares in Figure 2, is achieved if one instead assumes that beyond 2023 Block IIA interceptors are delivered at the same rate (52 per year) planned for Block IB Interceptors in the early 2020s.
Figure 2. Projected numbers of SM-3 Block IIA interceptors (red symbols) under low, medium and high assumptions and number of Block IB interceptors assuming a total buy of 396 and a fifteen year service life.
Figure 2 also shows (with blue squares) the projected number of Block IB interceptors assuming a fifteen year service life with deliveries ending in 2023. The numbers of Block IIA interceptors would likely be lower if deliveries of Block IB missiles continue beyond 2023 (or if their service life is significantly greater than fifteen years). Because of the lower cost of the IBs, it may be desirable to keep a mixed force of IBs and IIAs, however, as will be discussed in the next post in this series, there are strong reasons why the Navy may choose to procure more IIAs over any additional IBs.
(2) Projecting by Deployments
One data point that we have is that the United States plans to buy 182 Block IIA interceptors solely for the European Phased Adaptive Approach (EPAA). These missiles, to be deployed at the Polish and Romanian Aegis Ashore sites (up to 24 each) and on the four U.S. Navy destroyers now based in Spain, would support the EPAA though 2040. With a Block IIA lifetime of twelve years, not all of these would be deployed simultaneously, with the total deployed at any one time likely between 96 and 144.
It seems likely that a similar or even larger number of Block IIA interceptors will eventually be forward deployed in Japan. Currently eleven U.S. Aegis Ships are forward deployed at Yokosuka, Japan, seven of which are BMD capable. In addition, it can be expected that Japan, which is co-producing the Block IIA, will deploy a substantial number of them on its eight planned Aegis BMD capable ships, although I do not include these in my count here.
As noted in my previous post, the current Navy requirement (which will not be met until about 2026) is for 40 BMD “advanced” capability Aegis ships (capable of conducting air defense and ballistic missile defense simultaneously) – four of which are for the EPAA and nine of which are for forward deployment in Japan. Including the 21 Aegis Flight I and Flight II destroyers with a basic or intermediate BMD capability gives a total of 61 BMD capable ships in 2026. (No cruisers are included in this count be it is unclear/unlikely if any BMD capable cruisers will be in service in 2026)
If we then make a seemingly very conservative assumption that the remaining 48 of the 61 BMD capable ships will eventually deploy as many Block IIAs as the thirteen forward deployed BMD ships (plus the two Aegis Ashore sites), we get a total of 4*(96-144) = 384 – 576 deployed Block IIAs.
The point of this very rough projection by deployments is simply to show that medium and even the high projection in Figure 2 are more than plausible and that the United States is ultimately likely to deploy as many as 500 or even many more Block IIA interceptors. If the lifetime of the Block IIA interceptors is extended beyond twelve years, these projected numbers could be much higher. For example, if the Block IIA’s service life was extended from the presently planned twelve years to the twenty years intended for the now cancelled Block IIB missile, the medium equilibrium level in Figure 2 would increase from about 520 missiles to about 870. My next post in this series will consider some of the implications of deployments of such large numbers of strategic-capable interceptors.
I have added the following figure in response to a comment below:
 Ronald O’Rourke, “Navy Aegis Ballistic Missile Defense (BMD) Program: Background and Issues for Congress,” CRS Report 33745, November 10, 2015, pp. 14-15. Available at: http://fas.org/sgp/crs/weapons/RL33745.pdf.
 Department of Defense, Fiscal Year (FY) 2016 President’s Budget Submission, Missile Defense Agency, Procurement, Vol 2b, February 2015, p. 2b-14. Available at: http://comptroller.defense.gov/Portals/45/Documents/defbudget/fy2016/budget_justification/pdfs/02_Procurement/MDA_PROCUREMENT_MasterJustificationBook_Missile_Defense_Agency_PB_2016_1.pdf.
 A totals of eleven Block I missiles were built. Two were expended in intercept tests in 2005. The others had reached the end their service lives by 2009, although two were expended in intercept tests in 2011 (one of which failed).
 Jason Sherman, “DOD Reinstates Plan To Buy Nearly 400 SM-3 Block IB Interceptors,” Inside Defense SITREP, September 10, 2015.
 Twelve year service life from: Justin Doubleday, “Pentagon Will Buy Extra Block IIA Interceptors for European Missile Shield, Inside Defense SITREP, August 4, 2015
 In 2022, deliveries are projected to be 52 Block IBs and 19 Block IIAs, so the constant cost assumption gives a total of 26 + 19 = 45 Block IIAs per year. Assuming one missile expended in test per year and a twelve year service life, the equilibrium number is then 12 x 44 = 528. Block IB interceptors cost about $10-11 million each, while Block IIA interceptors are usually described as costing $20-25 million each.
 I have not seen a published figure for the Block IB service life, but it is likely to be significantly longer than the roughly ten year life for the Block IB. The projection does not include any Block IBs expended in testing beyond 2023.
 Doubleday, “Pentagon Will Buy Extra Block IIA Interceptors.”
 Ships at Yokusuka from “Commander Naval Surface Force, U.S. Pacific Fleet” at: http://www.public.navy.mil/surfor/Pages/PacificTheaterShips.aspx#.VqFISI-cGM8, plus the Barry which replaced the Lassen in early 2016. The BMD capable ships are the Shiloh, Barry (which is an advanced BMD capability, Baseline 9 ship), Wilbur, McCain, Fitzgerald, Stethem and Benfold.
 Japan currently plans to have eight BMD capable ships and has also expressed interest in deploying one or more Aegis Ashore sites. (http://news.usni.org/2015/05/18/house-paves-the-way-for-japan-to-buy-aegis-ashore-adds-anti-air-warfare-to-european-sites.)
 Prior to the cancellation of the Block IIB, the United States intended to buy only 50 Block IIAs for the EPAA. The increase to 182 Block IIAs after the cancellation suggests that prior the Block IIB cancellation, the plan was that relatively few Block IIAs would be built compared to the number of Block IIBs which would eventually replace them. In this situation the relatively short service life of the Block IIA may not have been a serious limitation on the number of Block II missiles the Navy could deploy. But unless a successor missile to the Block IIA is eventually built, a longer lifetime version of the IIA could be highly desirable.