The Tomahawk Land Attack Missile, or TLAM, is named after the Tomahawk — a Native American axe. If you have ever seen a Western movie, the tomahawk is thrown overhand, and can be quite dangerous as Ed Ames — who played a Native Amerian on the television program Daniel Boone — demonstrated on the Tonight Show with Johnny Carson:

As this little moment with Johnny suggests, when it comes to Tomahawks, aim is important!

I recently drafted a little memo on the Nuclear Tomahawk, the TLAM-N, and the problem of clobbering — when a Tomahawk missile goes astray. The short version is that Japanese officials should let the US retire the TLAM-N in 2013 because the possibility that it might crash in Japan or South Korea en route to targets in North Korea makes it all but unusable.

As this story in Kyodo News by Masakatsu Ota would suggest, the Japanese public would flip if they understood how TLAM-N works.

Below is an html version with hyperlinks. You can also download a pdf version with citations that looks more like an “academic” paper. It is still very much a draft; comments are welcome.

A Problem with the Nuclear Tomahawk

Jeffrey Lewis
December 14, 2009

As part of his September 1991 “Presidential Nuclear Initiatives,” President George H. W. Bush ordered the Navy to “withdraw all tactical nuclear weapons from its surface ships and attack submarines.” This included all nuclear-armed Tomahawk Land Attack Missiles (TLAM-N) deployed on US ships, including some Los Angeles-class attack submarines. Nuclear Tomahawk has been in storage since the Navy completed the withdrawal in early 1992. The Navy now wants to complete retirement of the system by 2013.

Some current and former US and Japanese government officials oppose retirement of the Nuclear Tomahawk. A Secretary of Defense Task Force criticized the Navy for assessing the weapon on grounds of whether it is “militarily cost-effective.” The Task Force argued that this criterion “ignores the weapon’s political value.” In other contexts, US and Japanese officials have argued that the credibility of the US nuclear umbrella “relies heavily on the deployment” of the TLAM-N.

This memo, using only unclassified information, explains in plain language why the Department of Defense should retire the Nuclear Tomahawk. One shortcoming of the Nuclear Tomahawk stands out: the possibility that a Nuclear Tomahawk would accidentally crash in an allied country like Japan or South Korea.

The problem is that the mid-1980s Tomahawk guidance system directs the missile to its target by comparing digital maps stored in an onboard computer against radar measurements of the terrain below the missile. The Nuclear Tomahawk, for example, needs to complete seven of nine “position-fixes” – matching a map to actual terrain — to arm the nuclear weapon. Each “fix” requires a map of rough and unique terrain approximately 7-8 kilometers in length. Since distinctive terrain is unusual by definition, the need for at least nine distinctive 8 km-long maps routinely results in routes of 100 km or more. Since terrain data must be extremely accurate, the Navy tends to prefer routes over friendly countries which allow the United States the access needed to make accurate maps in advance.

During the course of its flight along this “ingress route” a Tomahawk missile can drift off course and fly into the terrain that is supposed to guide it – an event known as “clobbering.” During the initial phase of Operation Iraqi Freedom in 2003, approximately ten conventionally-armed Tomahawk missiles went astray, crashing in Turkey, Saudi Arabia and Iran. In response to the political fallout from these stray missiles, the Navy suspended launches of Tomahawk missiles from ships in the Mediterranean and Red Seas. These Tomahawks were newer and had more modern guidance systems than the nuclear versions kept in storage since 1992.

(Vice Admiral Timothy Keating stated that “less than ten” out of 800 Tomahawk missiles (about 1.25 percent) “have been found in Turkey and in Saudi Arabia.” Other reports suggest the number of Tomahawks fired was 675, which would bring the total closer to 1.5 percent.)

Navy officials are rightly concerned about the political consequences if a US nuclear weapon were to fall in a friendly country like Turkey, Saudi Arabia, South Korea or Japan. The 1966 crash of a US B-52 bomber carrying four nuclear weapons near Palomares, Spain – which strained relations with US allies and eventually resulted in changes to US Air Force operational practices – remains a potent memory.

This problem is especially vexing in scenarios involving North Korea. Although North Korea is rugged and mountainous, it is also relatively small and surrounded by featureless water. For obvious reasons, the United States is unlikely to fly nuclear-armed Tomahawk cruise missiles over Russia or China. As a result, the most plausible ingress routes lie over South Korea and, to some extent, Japan.

It is very surprising that officials within the Japanese government have lobbied the United States to retain the Nuclear Tomahawk. If the Japanese and South Korean public understood how Nuclear Tomahawk works and that a failure might result in a nuclear weapon crash landing on their territory, the result would be a public relations nightmare. It is important to note that the Nuclear Tomahawk’s 150 kiloton W80 nuclear weapon would not detonate if it fell in South Korea or Japan while flying over either country. However, within Japan, even the possibility of Tomahawk overflights and crashes would raise sensitive issues related to the transit of nuclear weapons through Japanese territory and waters. Within South Korea, similar concerns would be complicated by the colonial overtones of Japanese officials pressing for Nuclear Tomahawk overflights of South Korea. The mere possibility of public disclosure alone ought to impel retirement of the Nuclear Tomahawk.

The Tomahawk Missile

The Tomahawk Land Attack Missile (TLAM) is a cruise missile that can be launched from US Navy ships and submarines. The missile was initially deployed in the 1980s. The original nuclear variant has a range of 2500 km.

The United States today has four types of Tomahawk Land Attack Missiles in its arsenal – three conventional and one nuclear. For convenience, this paper refers to the nuclear-variant as Nuclear Tomahawk. It is properly called TLAM-N – for Tomahawk Land Attack Missile – Nuclear. The other variants – the TLAM-C, D and E are referred to collectively as Conventional Tomahawk. (TLAM-E is sometimes called Tactical Tomahawk or TacTom.)

Figure 1: Tomahawk Cruise Missiles in US Inventory

Block Designation IOC Guidance Warhead
Block II TLAM-N 1986 INS, TERCOM W80 nuclear warhead
Block III TLAM-C 1994 INS, TERCOM, DSMAC, GPS 1,000 lb unitary warhead
TLAM-D 1994 Sub-muntions dispenser
Block IV TLAM-E 2004 INS, TERCOM, DSMAC, GPS 1,000 lb unitary warhead

Source: Raytheon.

As part of his September 1991 “Presidential Nuclear Initiatives,” President George H. W. Bush ordered the Navy to “withdraw all tactical nuclear weapons from its surface ships and attack submarines.” This included all Nuclear Tomahawks deployed on USN ships, including some Los Angeles-class attack submarines. All Nuclear Tomahawks have been in storage since the Navy completed the withdrawal in early 1992.

Over the same period, the United States has developed two successive generations of Tomahawk missiles (the Block III and Block IV) with improved guidance. One feature has been the integration of satellite guidance using the Global Positioning System. (The United States does not use GPS for nuclear weapons guidance due to concerns regarding jamming and spoofing.) Although some Block II Conventional Tomahawks remained in the inventory though the 1990s, U.S. regional combatant commanders strongly prefer the newer Block III version. In March 1999, Navy officials testified that about 90 percent of TLAMs used in recent military operations had been the Block III weapon.

Today, all remaining Block II Conventional Tomahawks have been converted to the Block III version. The Navy wants to complete retirement of the remaining Block II Nuclear Tomahawk systems by 2013

Figure 2: Block II Tomahawk Flight Profile

Source: GAO/NSIAD-95-116, Cruise Missiles: Proven Capability Should Affect Aircraft and Force Structure Requirements, General Accounting Office, April 1995, p.15.

Tomahawk Guidance

Nuclear Tomahawk uses a 1980s-era system called Terrain Contour Matching (TERCOM) to guide the missile over the majority of its flight. Launched from the sea, the TLAM flies a preprogrammed route to landfall and then starts matching the observed terrain, using radar, to maps stored in its onboard computers. The Nuclear Tomahawk, for example, needs to complete seven of nine “position-fixes” – matching a map to actual terrain – to arm the nuclear weapon.

Each “fix” requires a map of rough and distinctive terrain approximately 7-8 km in length. (Each map comprises approximately 64 samples of 122 meters-long strips of terrain.) Since distinctive terrain is by definition unusual, a collection of nine or more maps 8 km in length routinely results in routes that are hundreds of kilometers in length. Since terrain data must be extremely accurate, the Navy tends to prefer routes over friendly countries that allow the United States enough access to make very accurate maps in advance.

Despite claims of outstanding Tomahawk performance during the Operation Desert Storm, a subsequent analysis by the Center for Naval Analyses and the Defense Intelligence Agency raised questions about the effectiveness of the system. Although the analysis remains classified, a General Accountability Office report concluded, based on the CNA/DIA analysis, that Tomahawk “accuracy was less than has been implied.” Among the problems that GAO pointed to included “the relatively flat, featureless desert terrain in theater made it difficult for the Defense Mapping Agency to produce usable TERCOM ingress routes…”

The flat, featureless terrain between the Persian Gulf and Baghdad forced the United States to create “ingress” routes for Tomahawk missiles for Operation Desert Storm in 1991 that took the missiles over Iran Saudi Arabia, Syria and Turkey:

Yet other complications persisted. The gray steel boxes housing the missiles topside contained secrets to which few men were privy. One secret – which would remain classified even after the war – was the route the Tomahawks would fly to Baghdad. The missile’s navigation over land was determined by terrain-contour matching, a technique by which readings from a radar altimeter were continuously compared with land elevations on a digitized map drawn from satellite images and stored in the missile’s computer. Broken country — mountains, valleys, bluffs — was required for the missile to read its position and avoid “clobbering,” plowing into the ground.

For shooters from the Red Sea, the high desert of western Iraq was sufficiently rugged. But for Wisconsin and other ships firing from the Persian Gulf, most of southeastern Iraq and Kuwait was hopelessly flat. After weeks of study, only one suitable route was found for Tomahawks from the gulf: up the rugged mountains of western Iran, followed by a left turn across the border and into the Iraqi capital. Navy missile planners in Hawaii and Virginia mapped the routes and programmed the weapons. They also seeded the missiles’ software with a “friendly virus” that scrambled much of the sensitive computer coding during flight in case a clobbered Tomahawk fell into unfriendly hands. A third set of Tomahawks, carried aboard ships in the Mediterranean, were assigned routes across the mountains of Turkey and eastern Syria.

Not until a few days before the war was to begin, however, had the White House and National Security Council suddenly realized that war plans called for dozens and perhaps hundreds of missiles to fly over Turkey, Syria, and Iran, the last a nation chronically hostile to the United States. President Bush’s advisers had been flabbergasted. (“Look,” Powell declared during one White House meeting, “I’ve been showing you the flight lines for weeks. We didn’t have them going over white paper!”) After contemplating the alternative-scrubbing the Tomahawks and attacking their well-guarded targets with piloted aircraft — Bush assented to the Iranian overflight. Tehran would not be told of the intrusion. But on Sunday night, January 13, Bush prohibited Tomahawk launches from the eastern Mediterranean; neither the Turks nor the Syrians had agreed to American overflights, and the president considered Turkey in particular too vital an ally to risk offending.

The United States used the same “ingress routes” for conventional Tomahawk strikes in 2003, during the initial phase of Operation Iraqi Freedom. Between 1-2 percent of all Conventional Tomahawks were “clobbered” en route to their target in one of three countries: Iran, Saudi Arabia or Turkey. Additional missiles may have been lost over Iraq. The map below shows the ingress route and the location, based on press accounts, of six “clobbered” Tomahawks. It is worth noting that these crashes occurred involved newer Block III models of the Tomahawk missile that supplemented onboard TERCOM systems with satellite-aided Global Positioning System (GPS) guidance. The existing Block II Nuclear Tomahawks, which do not have GPS, would likely experience worse rates of clobbering. (Moreover, because GPS signals are subject to jamming and spoofing, the United States military has been reluctant to use satellite-guidance for nuclear weapons.)

Figure 3: Clobbered Tomahawk Missiles in Operation Iraqi Freedom

The crashes in Turkey and Saudi Arabia created difficult a political problem for the United States. According to one press account, locals pelted US vehicles with stones as US soldiers attempted to recover the clobbered Tomahawks in Turkey. The two images below show a clobbered Tomahawk, guarded by Turkish security forces and some onlookers who have gathered at the crash site. As a result of complaints from Ankara and Riyadh, the United States suspended Tomahawk launches from the Mediterranean and Red Seas in late March 2003.

Figure 4: A Clobbered Tomahawk Missile In Turkey

Credit: Mehdi Fedouach/AFP/Getty Images. March 29, 2003, Buyukmerdes, Turkey.

Figure 5: A Crowd Gathers Near the Clobbered Tomahawk

Credit: Mehdi Fedouach/AFP/Getty Images. March 29, 2003, Buyukmerdes, Turkey.

Issues for Japan and South Korea

Some officials have suggested that TLAM-N is the only unique, tactical nuclear weapon system that demonstrates the commitment of the United States to the security of Japan and South Korea. As a result, some Japanese Government Officials in Tokyo and Washington have pressed the Office of the Secretary of Defense to overturn the Navy’s decision to retire Nuclear Tomahawk.

North Korea has rugged terrain that is suitable for TERCOM mapping. According to the Central Intelligence Agency, North Korea’s terrain comprises “mostly hills and mountains separated by deep, narrow valleys.” However, North Korea is also small and surrounded largely by featureless ocean. At its narrowest point, North Korea is less than 200 km wide.

Although there may be some potential ingress routes involving the long finger of North Korea that extends to the northeast along the Sea of Japan, the need for highly accurate maps, proximity to the Chinese and Russian borders, and the preference for multiple axes of attack probably means that mission planners must consider some ingress routes that fly over non-North Korean territory.

For obvious reasons, the United States is unlikely to fly Nuclear Tomahawk over China or Russia. This leaves South Korea and, possibly Japan, as possible sources of terrain for TERCOM matches. It is important to note that the Nuclear Tomahawk’s 150 kiloton W80 nuclear weapon would not detonate if it fell in South Korea or Japan while flying over either country. As mentioned above, the Nuclear Tomahawk will not arm the warhead unless the onboard guidance computer successfully complete seven of nine contour matches – a condition precluded if the missile “clobbers” early in flight before the seventh match.

Even without a nuclear explosion, the political ramifications of crashing a nuclear-armed missile into a friendly country would be profound. A similar event happened in 1968 when a B-52 carrying nuclear weapons collided with an in flight refueling tanker over Palomares, Spain, dropping nuclear weapons into fields and the Mediterranean Sea. The incident created tensions between the United States and its allies, notably Spain, and – in combination with a subsequent accident at Thule, Greenland – led to the elimination of “Chrome Dome” flights with nuclear weapons.

Simple disclosure of this problem in the Japanese or South Korean press could create a political firestorm. The lobbying of one or more Japanese government agencies to maintain a nuclear missile whose mission would depend upon being able to fly over Japan and South Korea, which involves the risk of crashing in those countries, could lead to a severe political crisis, if the Japanese and South Korean publics became aware of these facts. In Japan, the issue of nuclear weapons transiting Japanese territory and waters is extraordinarily sensitive. Nuclear Tomahawk directly raises the issue of nuclear weapons transit, albeit in wartime, at a time when Japanese newspapers are publishing details of previous “secret” agreements between Tokyo and Washington regarding US nuclear weapons in Japan. In South Korea, where memories of Japan’s occupation have left a lingering sense of distrust, the revelation that Japanese bureaucrats are lobbying to retain a nuclear weapons system that would fly over South Korean homes and farms would deepen tensions between two important U.S. allies.

The mere possibility of public disclosure, therefore, ought to impel retirement of the Nuclear Tomahawk.