In 2012, then-President Barack Obama admonished the Syrians that any use of chemical weapons would be crossing a “red line” that would prompt U.S. military action. In 2013, the Syrians crossed that red line but later agreed, it had seemed, to destroy their stocks of nerve gas. The sarin attack on 4 April showed that President Bashar al-Assad’s government had lied, so the USS Ross (DDG-71) and USS Porter (DDG-78) fired 59 Tomahawk cruise missiles at a Syrian airfield from which the nerve gas attack against Syrian civilians had been mounted. The U.S. Tomahawk strike showed the Trump administration would take the red line seriously. By extension, the new administration demonstrated to others, such as the North Koreans, that it was more willing to take military action than its predecessor. The strike illustrated the strengths and weaknesses of cruise missiles, which have come to be a weapon of choice for the United States.
Tomahawk missiles were and are attractive for two reasons. The first is precision. If targets are all points whose position can be determined accurately, one or more Tomahawks can probably knock them out. The other is that a Tomahawk strike risks no aviators—no one can capture a Tomahawk and parade it through the streets before ransoming it or killing it. Think of the way in which the North Vietnamese made hostages out of captured U.S. pilots, or of the later capture of a U.S. pilot who was shot down during a strike in Lebanon’s Beqaa Valley. Pilots must sometimes be risked, but they should not be put in jeopardy lightly. It seems sensible to ask under which circumstances pilots should be risked. When is the pilot’s unique capability crucial? When is it enough for a distant targeteer to decide what to hit and how to get there? A Tomahawk cannot carry the bomb weight that an F/A-18E/F or an F-35C can, but a future cruise missile or an armed unmanned aerial vehicle (UAV) might.
The current Block IV version of Tomahawk is far more capable than the missile first used in combat against Iraq in 1991. The most important improvements are Global Positioning System (GPS) guidance and the ability to change targets in flight. The original Tomahawk relied on a series of altimeter readings, which it compared to on-board data to correct its course. To be sure it was on the right course it had to fly over land for much of its run to a target. Moreover, any area over which a Tomahawk had to be guided had to be mapped in great detail beforehand. The then-Defense Mapping Agency spent many man-days creating the necessary maps of Iraq before the 1991 war, as Iraq had never previously been considered a likely target area. Even then Tomahawks were given only a limited number of flight paths, for example as they approached Baghdad, and that made it possible for the Iraqis to concentrate their defenses in particular places, and to shoot down some U.S. missiles.
Conversely, once GPS guidance was introduced, Tomahawks could be fired against any chosen target. This capability was first demonstrated in strikes against Serbia in 1994. Later the missile was provided with a datalink: once the missile was aloft, a controller could designate a target (and presumably a path to it). Current Tomahawks also can relay target imagery back to their operators.
The result is an extraordinarily flexible weapon that is, in effect, a one-way UAV. The only significant difference is that the entire missile dives into its target rather than simply dropping a bomb and returning. If Tomahawk is now the weapon of choice for U.S. naval attacks, should its successor be an armed UAV? Compared to a carrier-launched UAV, Tomahawks seem to be limited in only one important way: they are fired from a destroyer or cruiser vertical launch system, which is nearly impossible to reload at sea. A carrier operating UAVs (or its usual manned aircraft) can easily reload its weapons. It therefore takes either a carrier or a very large surface force to attack anywhere on a sustained basis.
Viewing Tomahawks as one-way UAVs raises the question of how strike warfare should be divided between manned and unmanned aircraft. The Navy is purchasing the F-35 as its day-one attack bomber, which means that, thanks to its stealth, it can destroy enemy air defense systems that would prevent other aircraft from operating freely over enemy territory. These targets generally will be found, not by the bomber that hits them, but by separate reconnaissance systems, including satellites and electronic reconnaissance platforms.
It can be argued that only a human can overcome enemy jamming (for example, of GPS), the presence of which could make it impossible for a missile to find the target. Too, only a pilot has the judgment to distinguish among ambiguous targets. It probably would be unacceptable to bet on a real-time data link in the face of jamming. For example, only a pilot is likely to be able to say that a moving vehicle is a civilian bus rather than a missile launcher or a troop carrier.
It is not so obvious that such judgments will be crucial on day one, when the critical targets will be enemy surface-to-air missile systems, which must be temporarily fixed as they prepare to fire. It may be more profitable to improve the timeliness of remote observation of an enemy’s defenses. Should stealthy armed UAVs be the future day-one attack bombers?
Tomahawks have their limits. They are subsonic, because supersonic missiles would lack sufficient range. Are subsonic missiles inherently less survivable than supersonic ones? There is current interest in a Mach 3 alternative to the Tomahawk, particularly for antiship attacks. A supersonic missile dramatically reduces the reaction time available to the defense. At least in theory, a defending missile must be considerably faster and maneuver more violently—both requirements that considerably raise its cost. Against these virtues, a supersonic missile almost certainly must fly higher because its speed magnifies the effect of any momentary pitching movement and also magnifies low-altitude drag. The missile probably has to lock on to its target at greater range, to give it enough time to maneuver into it. Higher flight altitude and higher speed (which creates a greater infrared signature) combine to provide the defense with greater warning distance, though perhaps not time.
Current foreign missile programs seem to illustrate that this is by no means a settled question. Some years ago, the French tried and failed to sell a supersonic replacement for Exocet that they called ANS (Anti-Navire Supersonique). Instead they developed a stealthier longer-range (turbojet-powered) subsonic version of Exocet (Block 3) and a longer-range subsonic turbojet-powered antiship cruise missile, SCALP Naval. The current Norwegian and Swedish antiship missiles are both subsonic. So are most (but not all) Chinese antiship missiles. The Russians have and sell both subsonic and supersonic antiship missiles, as well as a compromise (Alfa) consisting of a subsonic missile with a supersonic final stage for the endgame. The only current supersonic land-attack cruise missile seems to be the Russian-Indian BrahMos. At present, the Russians are developing a hypersonic (Mach 5) cruise missile, but it is not clear how close it is to being operational. Since the collapse of the Soviet Union, the Russians have often obscured the line between a developmental (even paper) weapon and an operational one, sometimes in hopes of selling it and thus raising the funds needed to complete development.
Given sufficient range and information about target defenses, Tomahawks often can evade terminal defenses, at least on land. It is arguable that naval targets are a different proposition, since there are no hills at sea to hide an approaching missile. Current radars, however, generally cannot detect low-flying missiles at great range. The lower the missile flies, the closer the radar horizon. Radar horizon can be extended using exotic techniques such as high-frequency (HF) surface waves. The U.S. Navy tried this method in the 1990s but abandoned it because it demanded too much processing power. Moore’s Law may have solved that problem over the past two decades. Note that an HF surface wave radar generally detects its targets using their Doppler shift. The faster the missile, the easier to detect at longer range.
Finally, we can ask what effect did the Tomahawk strike in Syria have? The U.S. government said 58 of the 59 missiles hit their assigned targets. A Syrian opposition group saw 44 explosions, but some of the hits may not have been visible because the missiles may have penetrated hard structures and exploded inside. Russia downplayed the strike, claiming there were only 23 hits. Depending on who was reporting, the strike destroyed 15 or more Syrian aircraft. U.S. targeteers later said they avoided causing casualties (probably to avoid killing Russians on the base).
Unsurprisingly, the Syrian air base was back up and operating a few hours after the strike. A lesson of the first Gulf War (1991) was that despite considerable effort to develop runway-breaking munitions, it is difficult to put runways and taxiways out of commission for long. As a result, targeteers tend to avoid runways and target aircraft on a tarmac and command-and-control facilities. Hits on living quarters can kill pilots, who may be nearly irreplaceable for a regime like that in Syria. Ultimately, the Tomahawks did their job as well as any strike could have.
Dr. Friedman is the author of The Naval Institute Guide to World Naval Weapon Systems, Fifth Edition, and Network-centric Warfare: How Navies Learned to Fight Smarter Through Three World Wars, available from the Naval Institute Press at www.usni.org.
Photo credit: Raytheon