The sight of a Tomahawk missile leaving its launcher or flying over the landscape enroute to a target is now commonplace, but this extraordinary weapon just makes it look easy. The ability to hit pinpoint targets a thousand miles away with devastating accuracy did not appear overnight, and the weapons we see on CNN are nothing like the first versions that appeared in he early 1980s. Thankfully, for several reasons, these were never tested in battle.
USS Shiloh launches a Tomahawk during September 1996 as part of Operation Desert Strike
Origin
The Tomahawk concept originated in the 1970s, based partly on the success of the Harpoon missile, and partly from the then-ongoing SALT talks. An aerodynamic nuclear missile would be outside the scope of the existing SALT agreements. It would make a large number of naval platforms capable of strategic strike. This would vastly complicate the Soviet planners’ task of tracking and eliminating nuclear-capable platforms at the start of a conflict. Depending on who you talk to, this either increased the Soviet’s uncertainty level so that they would be more reluctant to begin hostilities, or it so threatened the Soviets with a dispersed nuclear capability that the delicate balance of nuclear deterrence was upset.
Description
All Tomahawk missiles have common features: A 21-inch diameter, folding stub wings, and a turbojet engine. Speed for all variants is 475 knots, or about Mach 0.7. They all fly at VLow altitude. A booster (different for ships and subs) propels the missile from its launch tube, then the engine starts and wings deploy, and the missile begins its journey. Part of the “cruise” in “cruise missile” comes from the fact that the missile’s airframe and engine are only designed for a “cruise” setting.
There’s no throttle, and the airframe works only inside a limited flight envelope.
All Tomahawk missiles can be fired by submarines from their torpedo tubes or special vertical launchers. Surface ships can either carry them in their Mk41 vertical launchers, or in Mk143 Armored Box Launchers. An air-launched version of the Tomahawk, the MRASM, was planned for the Air Force, but it was canceled in 1980.
Variants
The first version of the Tomahawk to appear was the Block I, which had two flavors: antiship (TASM) and nuclear (TLAM-N).
The BGM-109B Tomahawk antiship missile used the same seeker as the Harpoon missile and the same 1000-pound warhead as the Bullpup B. It first appeared aboard ships in 1982 and submarines in 1983. It had a range of 250 nm, four times that of the Harpoon and with a warhead twice as powerful. It had a selectable popup, like the later models of Harpoon. Although the nuclear BGM-109A has an earlier designation, it did not appear in service until 1987. It used combined Inertial and TERCOM (Terrain Contour Matching) guidance and had a W80 warhead, adjustable from 5 - 200 kilotons. Because the nuclear warhead was much lighter than the conventional warhead, the weapon could carry more fuel. It had a range of 1350 nm.
The TLAM-Ns were placed in storage in 1991, and TASM was withdrawn from the fleet in 1995. The Block II weapons were the first to carry a conventional warhead, allowing them to attack land targets without starting a nuclear holocaust. They featured several improvements, including DSMAC (Digital Scene Mapping and Correlation), and the ability to have waypoints over water.
The Block IIA BGM-109C (TLAM-C) carried the same Bullpup warhead as the TASM, and had a range of 675 nm. The weapon can attack by either flying straight into the target, executing a popup maneuver, or airbursting directly overhead. It entered service in 1986.
The Block IIB (TLAM-D) carried a submunitions dispenser with 166 BLU-97B Combined Effects Munition bomblets. It had a range of 472 nm, and entered service in 1988.
The Block IIIA and IIIB versions of the missile added a new feature: GPS. Combined with Inertial guid-ance, it almost completely removed the need for the DSMAC and TERCOM features, greatly simplifying the targeting process, as explained below. Best accuracy is achieved with at least one DSMAC image. The Block III weapons also use a smaller warhead, 750 lb of PBXN-107, which allows more fuel to be carried, and the range to be increased to 1000 nm.
Tomahawk Block IV was a planned Hughes/Raytheon improvement that would have added a terminal seeker, and UHF data link and other features, but the cost of the weapon became too high, and it was canceled in May of 1996. The newest version, which will be entering service soon (mid-2004) is the Tactical Tomahawk.
It will now be called the RGM/UGM-109E Block IV, although it is not the same design as the earlier Block IV missile. The Tactical Tomahawk has more features than a new Lexus. It has a UHF satellite link that allows it to be reprogrammed in flight to one of up to fifteen preset destinations, or it can be sent to any set of GPS coordinates. It has a TV camera, and can loiter over a designated area, allowing it to perform reconnaissance or BDA duties. It also costs half of what a Block II or III costs.
Just as importantly, it can be targeted by the launching platform, instead of by a shore facility, and it can be done quickly. More on this later.
Operational Use
Tomahawk Block II saw extensive use in Desert Storm, and while it did well, it did not do as well as the US would have liked. The limitations of the TERCOM/DSMAC guidance and the clumsy mission planning system became apparent. Its engine was also not powerful enough to climb in hilly terrain, which further limited the available routes.
Tomahawk Block III (with GPS) was used first in Bosnia and now in Iraqi Freedom. It is much more forgiving of the choice of flight path.
Guidance Types
All versions of Tomahawk’s guidance start with an inertial guidance system. This is not enough, though, because all inertial seekers suffer drift. 1970s inertial seekers suffered a cumulative error of about 1/2 nm per hour of flight. For a 1360 nm Tomahawk at 475 knots, by the time its 2 hour 50 minute-flight was over, it could be almost a mile and a half off target. This was not accurate enough, even for a nuclear warhead. TERCOM keeps the missile on course by taking a series of “fixes.” It compares a map stored in the seeker with the ground the missile flies over. The terrain, and the map the missile compares it to, has to be distinctive. The area looked at is larger than the stored maps, since it is expected that the missile will not hit its checkpoint dead on. If the terrain matches any part of the stored map, the missile can correct its course, resetting the drift to zero.
TERCOM is accurate enough for cross-country navigation, and can get a nuclear warhead close enough to do its job, but a conventional warhead needs more.
DSMAC does this by storing an image of the area before the target in the seeker’s memory, which the seeker can use to correct its final approach. The purpose is similar to TERCOM, but optical images allow a more precise fix.
The image must contain enough contrast for the seeker to recognize it, and changes can confuse the seeker. Recent camouflage, or even the effects of an earlier attack can change the target’s appearance enough to prevent the missile from getting a last-minute fix.
DSMAC II is an improved version that has a wider field of view and does a smarter comparison. It’s fitted to the Block III Tomahawks, along with GPS. GPS, or as CNN calls it, “satellite guidance,” allows the missile to determine its position in three dimensions. Combined with a smarter computer, the missile can adjust its course to arrive on target at a specified time. While the missile can make it attack on GPS coordinates alone, it can be combined with a DSMAC image for optimal accuracy.
Using Tomahawk in Harpoon
The four generations of Tomahawk show distinct levels of increasing accuracy and reliability, as well as highlighting the changes in computer technology over the past twenty years. Like a mariner, the Tomahawk navigates by comparing its position. These images had to be unique and easily recognized by the seeker’s limited computer. They also had to be gathered before the mission could be planned. While the United States planned operation Desert Storm, the National Intelligence and Mapping Agency (NIMA) was frantically gathering maps of possible checkpoints and images of potential targets. The 1991 war in Iraq revealed a weakness of TERCOM guidance.
Much of Iraq was featureless desert. There were few terrain features that were suitable for radar checkpoints. This meant that dozens of missiles had to use the same checkpoint, making flight paths so predictable that AAA could be stationed along the route. As a referee laying out a scenario, or a player who has Tomahawk missiles in his order of battle, there are several things that have to be dealt with: Block I is nuclear only. Without DSMAC, that’s all the accuracy the guidance system’s good for. Also, the missile can’t make a long overwater flight and hit a target right on the coast. Without a chance to correct any cumulative error, the weapon will almost certainly miss.
The flight plan for a missile depends on the potential launch area, defenses, prohibited or hazardous airspace (neutral countries, urban areas), as well as the target’s location. It has to be defined in three dimensions, and checked against intelligence for the location of air defense sites. As late as Desert Storm, it could take 72 hours to plan a single mission.
The missions were loaded on 80-pound disk packs called DTDs (Data Transport Devices) which were then physically transferred from one of the nine Tomahawk Mission Planning Centers to flagships and then to a Tomahawk shooter. The DTD can contain many, but not an infinite number of alternate targets, which are loaded into the missiles aboard the launch platform.
It wasn’t a quick process. It was feasible for preplanned targets, especially the potential confrontation with the Soviet Union. We may never know how many Tomahawk missions were prepared. The Kola peninsula alone could provide hundreds of aim points. A player’s targets will be handed to him at the start of a game, and he can’t change them. He may have a list of more targets than missiles, but he can’t add targets, and he can’t change their flight paths.
Block II weapons are similar, but in addition have the DSMAC imaging feature. This makes them accurate enough for a conventional warhead, but they won’t have the kind of precision we’re used to seeing from laser- or EO-guided weapons. Throughout the ‘80s and ‘90s, ways were found to automate the mission planning process. For Block II weapons, assume a planning time of 24 hours, and the requirement for the terrain maps and imaging remain. In a tactical game, the players will still have a fixed target and flight profile, but in a campaign or multi-day game, a player representing a theater commander will be able to request a few modifications to the list and expect to use them later in the game.
Block III makes it easy. A single GPS-defined coordinate and a DSMAC image of the target is all that’s needed for optimal accuracy. More GPS coordinates can be used for a complex flight plan that avoids prominent, but inconveniently located terrain features. At present, a Tomahawk mission plan can be completed in as little as two hours (But assume six hours for Block III mission planning). The planning cells have also moved to afloat units like carriers and other flagships, which means the local commander (the player) can do his own flight planning. Block IV Tactical Tomahawk will give the player even more options. He can send one missile in ahead of others to loiter and watch the others attack. If he sees the target is destroyed, he can retarget the rest, or make them abort. With Tactical Tomahawk, and continuing improvements in computers, targeting will be “near real time,” meaning minutes, rather than hours. A player may be able to target a dozen or more missiles during a long-term game. against a known feature. In Block I, this was radar maps of the terrain. In Block II, this added an image of the target area.
BT
Back to The Naval Sitrep # 24 Table of Contents
Back to Naval Sitrep List of Issues
Back to MagWeb Master Magazine List
© Copyright 2003 by Larry Bond and Clash of Arms.
This article appears in MagWeb.com (Magazine Web) on the Internet World Wide Web.
Other military history and related articles are available at http://www.magweb.com