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Aerospatiale unveiled its New-Generation Antiship Missile (ANNG) and OTO-Breda displayed its Teseo Mk 3 antiship missile at last October’s French Naval Exposition.
French Counter Sea-Skimmers
Three missiles displayed in model form at the October 1994 French naval exposition (Bourget Euronaval) illustrate particularly well likely future trends in antiship missiles. The Anti- Navale Nouvelle Generation (ANNG) [New-Generation Antiship Missile] is Aerospatiale’s attempt to develop an antiship missile from the rocket-ramjet technology already in service in the French ASMP hypersonic medium-range strategic missile.
Two others were alternative successors to the current Otomat, which arms Italian Navy ships and a variety of Italian frigates and corvettes sold abroad—as well as some French-built Saudi Arabian frigates and Egyptian and Saudi shore batteries: the Otomat Mk 3 and the Teseo Mk 3. The existing Otomat Mk 2 is the product of collaboration between Matra (France) and OTO-Melara (Italy).
The Otomat Mk 3 is the Matra version, whereas Teseo (named after the Italian version of the weapon system) has been proposed by OTO- Breda, a new team. Both proposed Otomat successors are subsonic.
The rationale for a supersonic antiship missile is that it is likely to smash through terminal defenses such as Gatling guns and that the missile’s high kinetic energy adds considerably to the warhead effect— by a factor of two or more, according to Aerospatiale.
Guns, such as Phalanx, fire in bursts, and as the closed-loop spotter operates on each burst; as the range decreases, each burst becomes more accurate. Eventually one round penetrates the target and, in theory, destroys it by fuzing the warhead.
Presumably burst length is set by spotting precision; too long a burst includes many rounds that have not been aimed properly. Since the rate of fire and muzzle velocity are fixed, the number of bursts depends on how long the missile spends approaching from maximum gun range to minimum acceptable range; doubling the speed of the missile presumably halves the available number of bursts, which worse than halves the probability of engaging the target successfully, since the accuracy of the bursts improves over time. Too, minimum acceptable range may increase, on the theory that even if the missile is destroyed, its fragments may have enough momentum to continue on and do serious damage. The higher the missile speed, the greater the momentum the fragments should have.
It probably does not help much to increase gun rates- of-fire, since the rate of bursts is set by the spotting cycle, and largely by the velocity with which each burst travels. Increasing the number of projectiles per burst, as in the new Italian Myriad dual Gatling gun, also displayed at Bourget, will increase lethality per burst, but probably not enough to offset a drastic reduction in the number of bursts the missile must
survive, because of the missile’s much higher speed.
Defensive missiles also should be affected. If their speed increases sufficiently, interception may require maneuvers more violent than they can undertake. Acceptable miss distances may also shrink. The blast and fragments from the warhead of the approaching defensive missile need a finite time to cover the distance to the target; the faster the target, the shorter the available time (to some extent, time can be recovered by triggering the defensive missile at a greater distance from its target).
These considerations suggest that the defense against a very fast antiship missile may have to be either a new kind of very energetic defensive weapon, perhaps more like one intended for defense against ballistic missiles, or some form of directed energy, or at the least a much higher-velocity gun firing guided rounds, simply to gain back depth of fire.
On the other hand, a supersonic missile is hardly likely to be very stealthy. Its radar cross-section may indeed be reduced, but it is likely to have a very strong infrared signature. To maintain high speed, it will generally need a very hot motor, producing an easily detected plume. High speed will induce considerable aerodynamic heating. Finally, the missile is likely to fly well above the surface to avoid accidentally plunging into a wave.
Aerospatiale representatives at the show claimed that the new missile was designed to meet an evolving Franco-German requirement for a weapon to outrange such current types as Exocet and Harpoon. The company has apparently abandoned its earlier rocket-ramjet Anti-Navire Supersonique (ANS), which was marketed as an Exocet successor; the ANNG presumably offers greater range, perhaps something like the 250 nautical miles claimed for the antiship subsonic version of the U.S. Tomahawk. Because it is at a much earlier stage than ANS, neither partner need invest very heavily immediately. Too, with the apparent shift in German naval interest toward foreign intervention, the Germans may be more willing to invest in a new- generation missile; they already operate Harpoons and early-model Exocets.
Aerospatiale implied that ANNG was competing with a subsonic alternative, possibly an upgraded Otomat. But the company also may fear competition from some version of the U.S. Tomahawk. The Royal Navy plans to buy 50 Tomahawks for its nuclear submarines, and surely a ship-launched version would be attractive. Once an export version existed, it probably would be offered to other NATO navies.
Both versions of Otomat reflect an alternative approach: the stealthy subsonic missile. Stealth requires both a small radar cross-section (or hiding a substantial cross-section in sea clutter) and a limited infrared signature. Otomat, Exocet, and Har-
91
Proreedinns / January 1995
The first of six Saab 340 airborne early warning and control aircraft is scheduled for delivery to the Swedish Air Force in 1996.
Swedes Buy Early Warning Aircraft
poon rely heavily on very low-level flight for stealth; it is easy to confuse the missile with sea clutter. In theory, only a pulse- Doppler radar—such as the U.S. Phalanx or Mk 23 Target Acquisition System—can break out the missile from the clutter. As for the infrared signature, the missile body is unlikely to show much aerodynamic heating. A jet-powered missile can cool its exhaust plume by mixing in cool surrounding air; a rocket-powered missile such as Exocet can use other shorter- duration techniques involving chemical additives. Since the defending radar already has some difficulty distinguishing the oncoming weapon, additional stealth measures, such as applying radar-absorbing material to the wing roots, should be quite effective. Finally, a subsonic missile may be better able to counter gun systems by maneuvering.
The Otomat Mk 3 is a digital version of the earlier analog Otomat Mk 2, using much the same airframe. An analog missile generally requires specific synchro inputs from its launch canister. It is therefore difficult to fire two different weapons from the same launcher. In contrast, different digital missiles are adapted relatively easily to the same launcher. In the case of Otomat, the same box can also launch the torpedo-carrying MILAS, the future French and Italian standoff antisubmarine weapon.
Digital missile tactics can be changed by changing onboard software. For example, it is easy to cause the missile to undertake evasive maneuvers near the target. Digital commands sent along the bus are converted to steering commands at the fins or into throttle commands at the engine.
More important, seekers can be changed, and that may have profound implications. Many current last-ditch defensive systems rely at least partly on an ability to recognize the incoming missile based on its electronic emissions—a far more difficult task if the seeker has been changed. It becomes even harder if each seeker is software-controlled, so that its waveform can be varied while the missile is in flight. Fully analog missiles are much more difficult to change.
The Mk 3 is, in effect, the simplest application of these ideas to an Otomat airframe. The company has decided that much more can be achieved by increasing missile intelligence, e.g., in the form of a better seeker, than by gross changes. Of course, it is still possible that simple stealth improvements have been made. It seems likely, for example, that some of the new software specifies the sort of terminal evasive maneuver already incorporated in the MM40 Exocet Block II.
The Italians went much farther with the Teseo Mk 3 while working within the dimensions of the existing Otomat launch tube, since any new missile would have to be deployed on board existing ships. Nevertheless, they designed a new hexagonal fuselage coupled with sharply swept wings. The new fuselage should reduce radar cross section from the missile’s beam aspect, since the upward- and downward-looking facets ought to reflect much of the radar energy striking the missile away from the transmitting radar.
The single radar dish in the nose has been replaced by a pair of sensors, a K-band radar above an infrared (IR) sensor. In theory, such a combination may be both stealthier and more reliable: stealthier because the active radar can be turned off near the target, leaving only a passive IR seeker, although even the passive seeker can be detected, by an IR sensor measuring its very cold temperature. The combination is likely to be more reliable than pure radar or pure IR simply because it is inherently more difficult to decoy.
The Teseo Mk 3 is credited with a range in excess of 160 nautical miles. Existing Otomats use mid-course guidance—either directly through a helicopter (the Italian Teseo system)— or by command from a ship using helicopter and other data such as the French Erato system on board Saudi frigates. It is not clear to what extent Teseo Mk 3 would be similarly guided. Presumably, one advantage of a supersonic missile is that information available at launch would suffice during the weapon’s shorter flight. If Exocets are well adapted to a target at 40 nautical miles, a missile four times as fast ought to be effective at 160 nautical miles.
The real promise of digital missiles is that they are relatively inexpensive to upgrade. At one time ships were upgraded, while missiles were considered not only expendable but short-lived. Times change. At a cost of about $750,000 each, 90 Standard Missiles (SM-2s) cost nearly as much as the Arleigh Burke (DDG-51) carrying them. Even the wealthiest navy must shrink
from buying such weapons as it bought disposable shells in the past. The implication of Otomat Mk 3 is that, once bought, an antiship missile airframe may last several decades; that it may be much easier to improve its lethality through intelligence than through changes in apparent performance. The two are not necessarily mutually exclusive: a smarter missile may, for example, be better at following a very low-altitude flight profile.
Aerospatiale, has realized exactly this truth in offering the Block II upgrade of the existing Exocet. It seems likely that the MM40 has a digital bus to the missile, so that it was relatively easy to replace the seeker and autopilot. It also was relatively easy to add some radar-absorbent material to reduce the radar cross-section.
Aerospatiale and the French Navy are offering MM40s in return for traded-in MM38s (earlier analog Exocets), which cannot be upgraded to the new stealthy configuration. The traded- in missiles are being issued to French warships, such as the Floreal-class frigates. It seems likely that most of the newly exported MM40s will be Block IIs.
As for supersonic antiship missiles, the threat has existed for years in the form of a variety of Soviet weapons such as the supersonic SS-N-22, the missile fired by Sovremennyy-class destroyers.
In October 1994, it was reported that the U.S. Navy would buy Russian rocket-ramjet Kh-31s (AS-17s) as low-altitude targets. Should they actually enter service, they should offer something of the performance of the proposed ANNG. At this writing there are reports that the Russian manufacturer is unhappy with the deal; it had hoped that the U.S. Navy would be adopting its weapon as a weapon, with all the prestige that would carry, rather than as a mere target.
Thus far, the Russian missiles pose by far the main supersonic antiship threat. The SS-N-22 (3M80) may have been sold in small numbers to Iran as a coastal defense weapon. Reports of a sale to India for the new Delhi class, however, seem to have been premature. India reportedly is developing its own supersonic antiship missile, presumably based on Russian technology. As for Western producers, ANS seems to have died and a supersonic Otomat successor—Otomach—never materialized.
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Proceedings / January 1995