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I wrote a blog post series about navy escorts in 2018 that IMO stood up to the test of time. Its conclusion/recommendation in the end is a tad radical and importantly, something that naval buraucracies won't like and some of them cannot afford. So I thought maybe I should revisit the topic and have a look at a frigate concept. Bear in mind I'm no specialised navy buff, but also bear in mind that so far all specialised navy buffs I discussed against failed to counter my arguments with arguments and resorted to logical fallacies instead.
Let's start with assumptions: A class of 4 ships for a small navy, serving primarily as oceanic escorts and secondarily as maritime blockade enforcers.
So overall size and mobility would be close to an improved Mogami class frigate.
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| Japanese Mogami frigate, full load 5,500 tons |
ASW (also see /2018/01/modern-warships-ii-asw.html)
A towed active/passive low frequency active sonar system (let's say CAPTAS-4) serves as main search sensor against submarines.
The sonar will detect many contacts, many of them false. All contacts close to the route of the ship/convoy will require investigation, while more distant ones require investigation only if they appear to move. Maps of known wrecks and seabed rocks don't help much, for submarines could still lie in ambush right next to them. (Some routes may be protected against this by deploying anti-submarine mines close to wrecks.)
The investigation of a contact can be done by cheap (not gold plated*) helicopter and by drone (with better range than possible with today's batteries alone). The minimum is two helicopters if you don't prefer drones, else one helicopter.
Both helo or drone could tow a magnetic anomaly detector in an attempt to pin down the exact location of the contact, but they could drop a miniature torpedo at the location ordered by the frigate even without a MAD confirmation. This torpedo would barely be dangerous enough to a submarine to provoke a detectable reaction. A miniature torpedo that fails to explode on the contact returns to the surface, floats and may be recovered, returned and its batteries recharged. The same could be done with small miniature torpedo/drone with side-looking sonar in the same format, but without warhead.
The helicopter and drone may also drop (and recover) active sonobuoys and serve as a radio relay for the communication between sonobuoys and frigate. No ASW computing or ASW decision-making onboard the helo.
A confirmed threat submarine contact on the other hand leads to a salvo of three anti-submarine missiles with each one lightweight torpedo as payload (minimum 10 in VLS) and evasive movement by the convoy. An accurate triangular impact pattern creates a no-escape zone for the attacked submarine and allows for a little inaccuracy of the detection. Coastal ASW could include the use of land-based anti-submarine missiles.
Survivability against torpedo attack would mostly be pursued via the usual means, possibly including miniature torpedoes for interception of heavyweight torpedoes (hard kill). The sonar would be very loud and the frigate has to escort loud and fast transport ships, so very costly measures for being very silent at low speeds are not justifiable.
To not use a hull-mounted ASW sonar may prove limiting in shallow waters, but those would be coastal waters and should usually be secured by other forces.
AAW: (also see /2018/02/modern-warships-iii-aaw.html)
A rotating inclined 3D AESA multifunction radar as the main sensor, datalink, two gimballed optronics sensor sets, passive detection and direction-finding of radar emissions are a good basic sensor suite. A smaller and cheaper rotating inclined 3D AESA multifunction radar (~Giraffe 1X) should serve as backup radar. I argue against expensive long range air search radars (American-style) because their range is even worse than that of a smaller rotating 3D radar's against seaskimming threats (bigger radar = mounted lower for better metacentric height). Distant high altitude threats can be detected by airborne radar (AEW) as well, which we need to improve detection distance against seaskimmers anyway. The main 3D AESA radar does need to be able to look up about 85° and does need to be able to detect incoming ballistic missiles, though.
An aerial drone may serve as a detection range extension against the seaskimmer threat, either free-flying or tethered (even towed). One should not expect much performance from the lightweight sensor suite and power supply of an affordable vertical landing drone design, though.
The longest-ranged air defence missile should be a VLS-launched SM-6 equivalent, present in small quantity (~8) more as a deterrent and anti-ship missile than for actual destruction of many aircraft or missiles.
Next, lock-on-after-launch area air defence missiles capable of both defending against platforms launching glide bombs (far, high, onboard countermeasures and capable of running at Mach 1+) or seaskimmer rockets (the classic Super Étendard+Exocet combo and some supersonic anti-ship rockets would have the launching aircraft below 200 ft altitude, subsonic and briefly at less than 30 nm distance) and against seaskimmer missiles is needed. This would preferably be a quad-packed (in VLS) equivalent to ESSM Block II; possibly IRIS-T SLX or CAMM MR. Minimum 20 missiles.
Third, a cheaper version of that missile for line of sight employment only with a cheap semi-active radar seeker (target illumination by the multifunction radar) equivalent to ESSM Block I would be advisable, but this is unnecessary if the previously mentioned LOAL missile uses a cheap-enough seeker (IRIS-T SLX?). Another minimum 20 missiles.
Finally, despite the stellar record of RIM-116 against test and training targets I prefer two 76 mm guns as close-in weapon systems for versatility and munition cost reasons. The forward gun should have much more ready munition than the usual 76 mm gun mount (rather ~200 than ~80) and water cooling to be able to fight of saturation attacks of cheap cruise missiles ("drones").
Drones with DRFM active radar decoy tech (~3DDS, towed drones), multispectral smoke and chaff should protect not only the frigate, but in containerised solutions also the protected transport ships (remote-controlled by the escorting frigates). The combination of radar and optronics for sensors and IR and radar countermeasures permits to deploy radar countermeasures against radar-using threats while shooting them with optronics-based fire control for guns and lock-on-after-launch missiles and deploying infrared countermeasures against IR-using threats while shooting them with radar-based fire control for guns and any missiles. The combination of both sensors and uncertainty would lead to either relying on datalink for LOAL misisle employment or maintaining a line of sight for the shipboard optronics sensors.
BMD (also see /2018/02/modern-warships-vi-other-topics.html)
A BMD hard kill requirement leads to multi-billion-Euro cruiser-sized ships and thier interceptor missiles (you'd probably use 3 per incoming missile!) are terribly expensive. It's very difficult to withstand saturation attacks due to the quantity, size and cost of interceptor missiles needed. Overall, hard kill BMD does not seem justifiable to me, especially for small budget navies.
Thus I propose to rely on soft kill for all aeroballistic/quasiballistic/hypersonic missile threats that cannot satisfactorily be defended against with the normal hard kill air defences.** Timely detection by the already mentioned rotating 3D AESA radar and warning via datalink and use of the aforementioned soft kill (decoy, multispectral smoke, chaff) capabilities against the threat from above are needed. Radar-detectable wake and waves should be reduced by becoming very slow, turning enough and finally stopping in time for the very brief period of the attack. One might also deploy chaff and offboard radar jammers to interfere with wake and wave detection by ballistic missiles.
BMDs have degraded sensing due to their high speed, they have extremely little time for sensing and they have (unlike seaskimmers) no chance to search a new target if they flew through a chaff cloud mistaken for the target. Soft kill has a good track record against non-ballistic anti-ship missiles, it's even more promising against ballistic ones. I would not trust onboard radar jamming due to the issue of home-on-jam guidance.
ASuW (also see /2018/02/modern-warships-iv-asuw.html)
The main ship killers in a war shouldn't be frigates, for ship killing should be the job of land-based airpower and possibly submarines. The exception would be boats showing up in coastal waters and auxiliary cruiser commerce raiders on high seas.
The longest-range SAMs (SM-6 class) and the guns would have some utility against ship targets, but additional ship attack missiles make sense.
A 127 mm gun could substitute for the forward 76 mm gun for more ASuW capability at the expense of more weight.
Land attack would be a secondary ability, but low priority for an escort. Eight NSMs should easily fit the bill regarding ASuW and land attack and could be eployed from their usual non-VLS launchers.
Mine countermeasures (also see /2018/02/modern-warships-vi-other-topics.html)
Naval mines are not much of a threat on the high seas and coastal naval mine threats should be handled by coastal forces. A hull-mounted mine avoidance sonar and divers suffice for the frigate (you need the divers anyway), especially if it has the side-looking sonar dfone for the submarine contact confirmation, for it would also be a minehunting drone. Minehunting beyond self-protection should be done with containerized land-based assets that can be mounted on a(n escorted) container ship as well.
You may have counted and come up with a minimum of 28 VLS + 8 NSM launchers. I consider 16 Mk 41 VLS as insufficient. You need more firepower to justify the expenses of a modern warship. 32 Mk 41 VLS is fine for a frigate IMO. The shortcut of avoiding the 10 VLS for anti-submarine missiles leads to a dependence on helicopters for ASW, which may not come close to being survivable enough. Additional VLS may be located on escorted ships in containerized launchers, under control by frigates via datalink.
I say a small power that cannot resist having a miniature navy of conventional warships should go for four general purpose frigates of about 6,000 tons at full load. Containerized minehunting, exogeneous AEW, land-based airpower, availability of submarines (or at least underwater drones) for ASW sparring, land-based replenishment and much else would be required in addition to the frigates. To only buy frigates without affording all else that it takes for them to be effective would be a waste of public funds.
I am opposed to buying 1+ billion Euro warships and strongly opposed to buying the excessively expensive hard kill BMD tech.
Likewise, I am strongly opposed to corvettes that are lacking in AAW and ASW, focusing on ASuW (which is best done by platforms other than ships). Corvettes are a waste of money.***
S O
edit: Kusha M3 might be the SM-6 equivalent.
https://en.wikipedia.org/wiki/Project_Kusha
*: Not a true ASW helicopter as we've seen them for decades, for these are horribly expensive and not survivable enough against possible use of air defences by submarines. Think of a MD500 equipped for finding/identifying/boarding ships in day and night (radar, flir, ropes, winch), capable of towing a MAD, carrying a 100 kg torpedo/drone and six ~16 kg sonobuoys. Beartrap, inflatable floats and at least partially folding rotor for naval use.
**: Very short ranged anti-ship ballistic missiles are rather similar to diving supersonic anti-ship missiles and could be defended against with the nomral area air defence SAMs if their developers paid a little attention to this scenario.
***: See also /2018/11/fixed-and-variable-costs.html and /2014/02/corvettes-and-air-defence.html
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