Naval air defence of the 2020's

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Currently navies use ship-to-air (surface-to-air) missiles of greatly varying sizes, ranging from shoulder-launched man portable ones originally developed for ground forces to missiles weighing more than a ton. Extreme ranges of a hundred nautical miles or more had been achieved in the 1950's already, but only so against targets in line of sight (flying high).

NATO used Sea Sparrow, SM-1, SM-2MR and SM-2ER missiles and a few competing equivalents by the end of the Cold War, but nowadays the big commercial successes appear to be RAM, Evolved Sea Sparrow and Aster. All area air defence missiles are nowadays expected to be available in a vertical launch version that does away with unreliable mechanical launchers and allows for a quicker sequence of firing.

The trend goes towards much better guidance or specialised missiles against guided ballistic missiles, and as a consequence individual missiles can have appalling costs.

ESSM Block 1 launch

There is one outstanding program that may become a true standard: RIM-162 Evolved Sea Sparrow (ESSM) Block 2. The original ESSM already excelled with its compactness, allowing four missiles to be packed into a single versatile vertical launch silo cell, unlike the French competition (Aster) that uses a too wide booster stage and is usually coupled with a vertical launch silo type used for the two Aster versions only.

missiles in vertical launch silos

Block 2 adds additional range (seemingly up from about 40-50 to about 80 km, but such published figures are unreliable and tell little anyway), more manoeuvrability and more importantly, a vastly improved seeker (active radar mode, semi-active radar mode and as I understand it also a home-on-jam mode, but the hardware would also be capable of an automatic command control mode).

The active radar will no doubt cost a lot (the missile may easily cost € 2 million in today's money), but it adds the ability to engage targets that are not in line of sight, but were reported through datalink by other platforms (ships, AEW aircraft). It also allows smaller ships to use this missile, for no dedicated target illumination radar or powerful-enough multi-function radar has to be carried for the target illumination as with ESSM Block 1's semi-active radar terminal homing.

The increased range finally may bring ESSM Block 2 into the range class of an Aster 30, which is recognised as an area air defence missile. In the 2020's an area air defence missile may be quad-packed into standard vertical launch silos. This may change a lot.

For example, ships specialised on the anti-submarine warfare (ASW) mission could still be part in the task force's area air defence plan with a substantial footprint (against very low-flying targets comparable to what 1990's dedicated air defence destroyers achieved). Their most substantial shortcoming compared to dedicated anti-air warfare destroyers would be a weaker radar suite, but this might matter little in a networked task force with AEW support.

ESSM Block 2 could thus do no less than end the era of separation between ASW and AAW frigates and destroyers in Europe without requiring the expense of very large (8,000+ t) combined ASW+AAW destroyers (as preferred by the USN since the 80's at the latest). A frigate of 5,000 t with all the typical anti-submarine warfare specialisations might still double as a powerful area air defence asset. The two paths would be joined through the characteristics of a (by comparison to a ship) tiny missile.
GP (general purpose) frigates may become dominant European designs in the 2020's instead of jack-of-all-trades-master-of-none export warships as they have been so far.

A missile which requires no target illumination radar could also be fired from inside a container carried by a mere cargo ship, of course. This may particularly be used as a second missile defence layer. GP frigates surrounding a convoy could form the first layer, and the escorted cargo ships would be platforms for the second layer. The old layered defences with some extended range missiles such as SM-2ER as an outer layer in addition to medium range missiles never offered much depth against seaskimmer missiles. The "extended range" applied to high-flying targets only because their terminal semi-active radar homing required a line of sight between ship and target.

Important for the area air defence capability will be the actual engagement envelope. This is a very tricky story, even if we ignore the very tricky radar physics and poor reliability of published range figures. I take two graphs from here to illustrate this:

(note the waist: The smallest width of the dark brown area is the part of an air defence perimeter's circumference that the air defence system may cover well. This important metric is very different from the "range" figure and never published. It also depends a lot on the target, particularly its altitude, speed, changes of course and evasive manoeuvres capability.)

(this gap exists mostly for short range SAMs)

A missile with a published range of "80 km" may effectively protect other ships against missiles passing at a distance of 20 km at low altitude, but maybe the correct figure is "30 km", or "40 km". It won't be "80 km", though. At least the active radar seeker offers the possibility of engaging very low targets beyond the horizon (if the rocket engine offers enough energy for it).

The dual-mode seeker will likely retain the capability of Sea Sparrow and Block 1 ESSM to engage ships and boats. The damage done to a warship by the small warhead can be substantial and vastly degrade its ability to defend itself, as evidenced by two accidental hits of a cruiser by two Shrike missiles (which were closely related to Sea Sparrow) in 1968 and an accident with Sea Sparrow hitting a Turkish warship in 1992. ESSM has demonstrated its ability to hit small fast-moving boats and is no doubt difficult to defend against when employed to disable a warship in a surface engagement. Meanwhile, the Block 2 missile could with its passive radar homing capability be used to suppress a hostile ship's radars* for a crucial few seconds in a synchronised attack with anti-ship cruise missiles (substituting for an anti-radar missile) - if and only if the ship radar's frequency range is covered by the ESSM Blk 2 seeker.

This goes way beyond what utility the Aster appears to promise (assuming the Block 2 missile will be completed and be effective at all, of course).

One of ESSM's known strengths is its spectacularly small minimum engagement range. This is apparently a few hundred metres (possibly only in easy scenarios), while Aster 30 with its booster had such issues with short range that the Aster 15 version with shorter range and shorter minimum range had to be developed.

A very short minimum range may make dedicated short range missiles unnecessary, which affects the RIM-116 Rolling Airframe Missile. This missile has racked up an impressive reliability and hit record in test firings, but it has a possibly fatal flaw: It (almost certainly) cannot reliably defend against an infrared guided anti-ship missiles such as NSM. Its passive radar seeker capability is useless against it, and its own infrared seeker almost certainly cannot sense a missile incoming from the direction of a dawning sun.

The ESSM Block 2 may thus become an all-in-one answer to naval needs for defence against aircraft and air-breathing missiles for the 2020's.

Meanwhile, dedicated, very large and very expensive missiles such as SM-3 may be used to provide a defence against guided ballistic missiles and an engagement capability against low orbit satellites. Even a  10,000 ton warship struggles with the mass, volume, topweight and electrical power hunger of a long-range ballistic missile defence radar, though. Dedicated BMD warships could resemble more a LPD-type ship than the slimmer frigates or destroyers.

A convoy escort group could have one such BMD ship that also serves as replenishment ship and helicopter carrier (AEW helicopter) as its core among the escorted ships, and general purpose frigates surrounding the convoy with gapless overlapping low frequency active sonar search and area air defence zones. That's but a possibility, of course.

There will likely still be an interest in some short-range weapon, and I suspect the classic 76 mm naval guns with their extreme rate of fire (for a short time) would still fit this bill without the expense of developing and deploying some gold-plated short-range missile or a range of specialised short range missiles. Nowadays these guns can even employ guided projectiles.

SM-3 / ESSM Blk 2 / STRALES - a possible AAW trio for a well-funded navy of the 2020's. It could greatly change some warship categories as they were known since the 70's (and thus the face of European navies).

I didn't cover fighters / interceptors yet, though they will also be relevant to naval air defence. A task force of frigates protecting a convoy may have a flight of potentially helpful fighters nearby, but even four fighters would carry anything ranging from two dozen to three dozen relevant missiles, while a frigate flotilla may have two hundred or more relevant missiles. The fighters' utility could be larger than these figures suggest because they could by virtue of their speed engage the missile launch platforms (combat aircraft) instead of the munitions (anti-ship missiles), of course.

related:
2009-04 SAMs with active radar homing
2013-01 Naval and air warfare; the problem with technology assessment (see the final part of this!)

S O

defence_and_freedom@gmx.de

P.S.: In case you wondered: No, I still don't think surface warships are relevant for alliance defence in the Baltic Sea and I don't think they're very important in the Mediterranean Sea either. Russian air power could wipe the Eastern Baltic Sea surface clean no matter what air defences the ships have. 

*: If and only if it uses the right frequency band!

edit June 2017: I overlooked AMRAAM-ER, a AIM-120 seeker mated to a ESSM rocket. It should be very close to the projected ESSM Blk 2. I wonder what the differences are going to be, save for a bigger antenna. Maybe ESM Blk 2 gets an AESA antenna?

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