In November 2016, the Navy cancelled development of the Long- Range Land-Attack Projectile (LRLAP) intended for the 155-mm guns on board the new Zumwalt (DDG-1000)-class land-attack destroyer.
Instead these ships will fire a modified version of the Army’s Excalibur guided shell. Because Excalibur is associated with a much smaller propelling charge, range will be considerably less. The cancellation was explained by cost escalation, as so few LRLAP shells were needed for the three-ship Zumwalt-class (originally planned as 30 ships).
The LRLAP cancellation occasions a look back to the relative values of guided shells and missiles on board ships. Excalibur is one of several alternative precision munitions. The LRLAP rounds reportedly cost $800,000 to $1 million each. Excalibur rounds are $70,000 each.
How valuable is a guided shell in a naval (largely shore bombardment) context? Do guns have virtues not connected with such munitions? Excalibur itself was conceived for land-based artillery. In that role, the virtue of a guided shell is obvious. In land warfare, logistics rules. Anything that reduces the total weight of shells that have to be carried is valuable. Even if individual shells are costly, a dramatic reduction in the number that must be fired to guarantee a hit is worthwhile—hence the development and widespread deployment of guided artillery and mortar shells.
A naval gun requirement is a bit different. Ships easily can carry hundreds of shells. Typically guns are a low-cost alternative to missiles, each of which may cost a million dollars or more. It is easy to imagine that shells are cheap because they are carried in large numbers, but they are not necessarily inexpensive, as the LRLAP saga shows. Compared to a missile, a gun/shell combination should be more economical because so much of the system (the ship’s gun tube and fire-control mechanism) is not thrown away each time a round is fired. The question is how much technology has to go into each round. For “smart” rounds, the guidance system built into the shell has to survive the enormous shock of firing, which is inherently expensive.
In the 1980s, there was intense interest in an infrared-guided version of the standard 5-inch shell to be used as a last-ditch air defense weapon for the Navy. The idea was that standard guns could fire at least ten such rounds a minute. In theory, existing gun fire-control systems would point the gun. The project died when the cost per shell turned out to be about $40,000, rather than the desired $10,000. At the time, the Standard Missile for air defense cost about $600,000, so one might ask why $40,000 was too much. The standard magazine load-out on board many Navy ships was 40 air defense missiles—or $24 million. A ship’s 5-inch gun magazine had about 600 rounds—also $24 million. It did not seem cost efficient to lock up a missile-magazine-worth of money for an inferior last-ditch defense.
LRLAP and Excalibur, in contrast, are conceived not as supplementary air defense but as a means of precision shore bombardment—naval gunfire support—using GPS guidance to hit targets designated by forward observers, aircraft, or unmanned aerial vehicles (UAVs). The gun tube and the shipboard fire-control system have to place rounds close enough to the target that the shell’s on board system can take over. Clearly it is less expensive to fire a single shell than a single longer-range cruise missile. Probably more important, shells—but not missiles—can be transferred routinely during replenishment at sea. A ship performing naval gunfire support can remain on station, conducting her mission, for a protracted period, whereas once a ship fires her missiles she must withdraw to reload in port.
This could be a decisive consideration, except that the U.S. Navy has another precision strike system that can be replenished easily at sea—the aircraft carrier. Like a gun, an aircraft carrier employs a mainly reusable weapon launcher, in this case an airplane. It might be argued that a future armed-attack UAV would be an even more economical means of shore bombardment against point targets. Incidentally, a single GPS-guided bomb (such as a Mark 80-series bomb equipped with a Joint Direct Attack Munition [JDAM] kit) costs less than a single GPS-guided Excalibur shell, although the bomb is considerably bulkier and packs a bigger punch.
The existence of aircraft carriers helps explain why the Zumwalt-class was not built in large numbers. The ship was conceived not as a general-purpose destroyer but rather as a “land-attack destroyer,” a concept that originated not in the Chief of Naval Operation’s staff (OPNAV) but in Naval Sea Systems Command (NAVSEA). Normally NAVSEA develops ships to meet OPNAV requirements; in this case the process was reversed. As the design proceeded, other features were added to provide a degree of general capability, but the basics of the design were dictated by a shore bombardment mission. The ship is stealthy to make her difficult to detect near an enemy coast, and she has a higher than usual degree of survivability (including peripheral missile launchers, so that one hit could not touch off a mass detonation). The original justification advanced by the ship’s NAVSEA sponsors was essentially that a mass of Tomahawk land-attack missiles could add decisively to the destructive power of a carrier battle group. The advent of GPS-guided bombs made the carrier’s aircraft capable of hitting multiple targets per sortie. Less than 100 additional Tomahawks seemed less valuable to the carrier strike group than when the concept was proposed in the mid-1990s.
It is also not clear how much the heroic efforts to make the ship stealthy will buy. For example, the Zumwalt cannot avoid leaving a detectable wake. High-frequency surface wave radars, which many countries (including Canada and China) operate, will not be affected by careful shaping intended to defeat higher-frequency systems. The shaping is likely to defeat the terminal sensors of current radar-controlled antiship missiles, but it is not clear how well the ship will perform against infrared missiles such as the Kongsberg Naval Strike Missile or against missiles using optical sensors. We can say that a great deal was sacrificed to gain the degree of stealth the ship possesses. That sacrifice was reflected both in the great size of the ship and in her high cost. Ultimately the oddly inverted requirement process for the ship’s design made the OPNAV staff less than enthusiastic when the ship’s cost became obvious; this class of ships was too specialized to be worth buying in numbers.
That leaves the only unique feature of the Zumwalt’s armament: her two automated 155-mm guns with GPS-guided shells. The question must be whether those shells are, or were, worth the price of the ship. There is no question that Excalibur works. Unfortunately, to hit a target on shore, the ship has to come within 25 miles of the coast. That might mean coming within mineable waters, or within range of swarm boats whose weapons are aimed by eye, hence not affected by antiradar measures. How valuable are a few hundred precision rounds under such circumstances? To what extent is the Zumwalt a missile shooter with a supplemental gun?
One of the major engineering features of the Zumwalt is her integrated electric power plant. Integrated electric drive has numerous virtues, which is why existing destroyers are being retrofitted with it. In the case of the Zumwalt, however, the rumored justification was that given sufficient electric power the ship might be able to accommodate revolutionary new electric weapons, such as the railgun. The shell fired from an electromagnetic railgun leaves the barrel at speeds up to Mach 6. It uses no gunpowder or other chemical propellants, which reduces the amount of explosive stored on board ship. Even the shell carries no explosive—it simply hits a target at high velocity and imparts impressive kinetic energy to the target.
As usual with new technology, there are challenges. The railgun accelerates its projectile down a highly charged path whose elements try to pull themselves apart from each other. That is why firing dozens of consecutive shots is considered a triumph at this stage. To be competitive with conventional guns, a railgun would have to fire hundreds of shots before requiring replacement. How excited would the Marines be about a naval gunfire ship that could fire only a few dozen rounds?
There is also interest in the railgun as an air defense weapon, exploiting the very high velocity of its projectile (i.e., very short time of flight) as a means of simplifying the fire-control problem. Such a weapon would work much like the current Phalanx close-in-weapon system: firing a shell, estimating its trajectory, and correcting for the next shot. The question would be whether the railgun could fire rapidly enough to make this closed-loop fire control effective. Note that although Phalanx often is said to create a wall of lead through which a missile must fly; in fact, it fires in bursts, which it tracks. A railgun equivalent to Phalanx would replace bursts with single projectiles. Some current antimissile guns in foreign navies already do that.
So where does this leave the naval gun? For years, medium-calibre naval guns have been valued not as a means of precision attack, but as a means of low cost attack. Firing a shot across the bow of a potentially hostile ship is still a worthwhile option—an option that probably will gain value in an increasingly unsettled world. Firing a few rounds ashore is still a useful demonstration of intent. The question remains whether precision, long-range strike from a naval gun is worth the cost, especially when the Navy has other means of precision strike. It might be more valuable to build an inexpensive GPS-guided bombardment rocket with a 60-mile range, which a surface ship could carry in numbers.
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.