Sunday, January 16, 2011

Artillery Rockets and Ballistic Missiles as Anti-Ship Weapons

Artillery Rockets and Ballistic Missiles as Anti-Ship Weapons

***This is a compiled and revised version of the several pieces posted this summer***

107 mm Artillery Rockets
Iran uses the 107 mm artillery rocket as direct-LOS anti-ship weapon. The 107 mm rockets are mounted on the large number of small high-speed patrol boats (HSPBs) which make up the numerical bulk of the IRGCN including the various RIB and MIL type boats manufactured by the Marine Industries Group (MIG).

While they might have a theoretical range of more then 8 km, it is unlikely that the effective range of an HSPB swarm armed with them would be, at the absolute maximum, more then a kilometer due to requisite proximity needed to ensure a hit on target. Furthermore, what with all the jostling about on small fiberglass hulled boats, accuracy is predictably abysmal. 

Generally speaking, on the 'Boston Whaler' type boats, the rockets are fired from 12-round launchers identical to the Chinese designed Type-63 launchers used by ground forces. However, others are fitted with either 11 (pictured right) or 19 round launchers optimized for naval warfare; these are electronically controlled, possibly with gyro-stabilization.

IRGC light patrol boats armd with DShK machine-guns and 11-round 107 mm rocket launchers (Fars News)
These types of rockets pose very little threat to modern warships, if only because their use necessitates extreme proximity, exposing them to the full range of defensive weapons mounted on today's frigates and cruisers. However, if by some miracle, a swarm of these boats was able to attack a military vessel, the amount of rockets used could inflict some damage, although because the damage would be spread over numerous smaller wounds above the waterline, it would unlikely to be fatal.

However, the real threat stems from their potential use against commercial shipping. Against thin-skinned, lumbering tankers, these small rockets could be particularly effective, even if they still lack the ability to sink a tanker. 

Small boat attack on an oil tanker with small arms and rockets during the Iran-Iraq war (Youtube/Iranian TV)

122 mm Artillery Rockets
122 mm rockets are used to a small degree on Iran's transport ships as well as the C-14 “China Cat” patrol boats. However, since they are used to such a small degree and on platforms unlikely to be part of a concerted anti-ship attack, they are not likely to be a major factor and shall be avoided except to say they would not make particularly effective attack craft by any interpretation.

IRIN "Takavaran" on board a China Cat (IRNA)

Fajr-3 / Fajr-5, and Zelzal Artillery Rockets
The larger caliber artillery rockets are not used in the direct-fire role, but rather as actual artillery, used in conjunction with conventional AShMs as a standoff weapon. While they have only been seen deployed alongside actual AShMs, its possible they could be used as a stand alone weapon.

However, it is worth noting that they might not even be used in the “anti-ship” role. Rather they might be fired in conjunction with AShMs in order to overwhelm a ships defenses without the intent for the unguided rockets to actually damage the ship. The challenge here would be to correctly coordinate the waves of rockets and missiles.

Tactical ballistic missiles on the other hand have never actually been alluded to by, or seen in service with the Iranian military in this role, however, it makes an interesting thought experiment given that Iran is known to operate both large calibre MLRS's as well as ballistic missiles in the anti-ship role.
Fajr-3 (Fars News)

Caliber: 240 mm
Max Range: 43 km
Warhead Weight: 90 kg
CEP: ~500 m*
Rockets per Launcher: 12

Fajr-5 (Mehr News)
Caliber: 333 mm
Max Range: 75 km
Warhead Weight: 175 kg
CEP: ~500 m*
Rockets per Launcher: 4

Zelzal-3/3B (Fars News)
Caliber: 616 mm
Max Range: 200 km
Warhead Weight: 950 kg
CEP: ~1000 m*

Caliber: 616 mm
Max Range: 260 km
Warhead Weight: 600 kg
CEP: ~1300 m

*CEP =Circular error probability – measure of accuracy / the radius of a circle that 50% of all projectiles fired, will fall into.

The most common payload is a unitary HE warhead, though cluster munitions are also likely in the Fajr-series, and possible in the TBMs. With regard to the behavior and specifications of the submunitions, I am using the “RAND model” established in the RAND Corporations 1999 paper detailing the possible threat to large bases and airfields by sub-munition dispensing ballistic and cruise missiles. 

Specifically, I assume that each sub-munition, or bomblet weighs .45 kg and that 25% of the warhead weight is devoted to the dispersal mechanism. This means that each bomblet threatens a 149 sq m area (with a 6 m lethal radii). This reflects normal behavior for submunitions used throughout the world in artillery or air-dispersed systems

(Google Earth)
The short range of the Fajr-series means that if situated on the coast, they would only be able to fire at the maximum range of their effectiveness, and then, only at certain chokepoints in the Persian Gulf. One solution would be to put them on islands where they could overlook shipping lanes. The disadvantage to this of course is that it makes them very easy to hunt.

TBMs on the other hand threaten all of the Persian Gulf, with shorter ranged systems still well within range of most traffic. One factor to consider is minimum as well as maximum range. In order to keep certain zones within range, the TELs would have to remain in a geographical “belt”. 

One potential problem would be the question of target acquisition. For effective targeting beyond visual range, both the MLRSs and the TBM's would require input. One possible manner is a basic maritime surface-search radar, the same that might be found on any yacht or cruiser. While not very accurate and without the ability to actually target the weapon, the one advantage is that it wouldn't register as a threat for any aircraft flying overhead looking for a target to shoot at; this system has been displayed on several types of stand-alone AShM launchers. During the Great Prophet 5 wargames in Spring 2010, the Fajr-series MLRS's were seen with data-link antennae which could indicate that they receive their targeting information data from other sources such as dedicated AShM's. Iran is also reported to have extensive combat networking capability within the Persian Gulf. Of course the fundamental problem of the rockets themselves being overly inaccurate mechanical systems persist.

The next part of this equation is the target itself. The only target worth considering is the largest of the large, in this case, a US Nimitz-class aircraft carrier which has a length of 332 m with a beam of 76 m in the shape of a large rectangle. The vessel has a top speed of 56 km/h though it might be more realistic to assume 1/2 or 3/4 speed, (28 and 42 km/h respectively). It is possible to lead the target, but it introduces another layer of complexity that tends to get magnified when dealing with imprecise instruments like surface-search radars and simple mechanical traversing controls.

So, what are the chances of either an MLRS or TBM being used to effectively attack a naval target?

After crunching the numbers we come up with some interesting results. Keeping in mind these are best case scenarios which involve a static target (unlikely), perfect targeting data (unlikely) and allowing a fair amount of leeway when it comes to unknown (unlikely).

Unitary Warhead: 90 kg, 35 m**
Cluster Warhead: 148 bomblets, 57 m spread*
(Google Earth)

Unitary Warhead: 175 kg, 44 m**
Cluster Warhead: 289 bomblets, 112 m spread*
(Google Earth)

Unitary Warhead: 950 kg, 78 m**
Cluster Warhead: 1,575 bomblets, 261 m spread*
(Google Earth)

Unitary Warhead: 600 kg, 67 m**
Cluster Warhead: 1,000 bomblets, 167 m spread*
(Google Earth)

 *Spread = Radius of circle formed by lethal zones of bomblets
** = Radius of lethal circle formed by unitary warhead

For comparison, here are the total threatened areas created by each permutation:

What's clear is how much more efficient cluster munitions are as the warhead increases in size, from 434% more efficient at the level of the Fajr-3, up to a whopping 962% more efficiency at the size of the Zelzal-3.

Also important is the size of the volley. The Fajr-series have multiple rockets that can be launched in close proximity to another. The TBMs on the other hand are restricted to using larger formations of TELs to increase fire power – with the exception of certain prototype Zelzal launchers – but these shall be ignored for now. A full volleys worth of rockets is represented by the 2nd, parenthetical number in the entry's below. 

Unitary: 3,972 sqm (47,664 sqm)
Cluster: 17,278 sqm (207,336 sqm)
Percent Change: 434%

Unitary: 6,189 sqm (24,756 sqm)
Cluster: 33,737 sqm (134,948 sqm)
Percent Change: 545%

Unitary: 19,110 sqm
Cluster: 183,868 sqm
Percent Change: 962%

Unitary: 14,070 sqm
Cluster: 116,741 sqm
Percent Change: 829%

sqm = Square Meters

Assuming Iran can actually hit an aircraft-carrier with sub-munitions however, what kind of damage could they do? After all, sub-munitions increase the chance of hitting the target, but they necessarily degrade the power due to the obvious fact that they fragment the warhead.

The hypothetical target in this case is CV-75 / USS Harry S Truman, a Nimitz-class supercarrier as a stand in for a similarly sized carrier passing through the Persian Gulf.
(Google Earth)

It doesn't look very impressive considering each only weighs around half a kilo. However bomblets are often deadlier then they appear, a .45 kg AP bomblet similar to the US BLU-77/B could likely, if only just, penetrate the flight deck of the carrier. Of course, this wouldn't deal permanent damage to the ships but could heavily damage any aircraft which are on deck at any given time. Furthermore, the shrapnel could damage radars, communication masts, kill personal and spray FOD over the flight deck which would require cleanup efforts that would further prevent combat sorties.

Shahab Ballistic Missiles
While China might be sweeping the headlines for their famed “carrier killer” ballistic missile, Iran similarly may deploy their ballistic missiles in an anti-ship role. In November, 2006, Then-General of the IRGC, Yahya Rahim Safavi had this to say on the subject in an interview on Iranian channel 2 TV:

"The Shahab-3 missiles has a cluster warhead and and consequently, it's destructive power exceeds several kilometers, because the warhead spreads into bomblets. It can be used against large bases, large concentrations of people, aircraft carriers, even against aircraft carriers because it explodes from above so it can completely destroy an aircraft carrier with it's planes."

So, while it's not the same as China's program for sure, it still represents an interesting strategic choice. Furthermore, given China and Iran's cooperation in the anti-ship weapon development, one shouldn't be quick to ignore the 'coincidence' that both countries are pursuing roughly the same path.

The Shahab-3, a relative of the SCUD family, has two main variants that Safavi could have been talking about in 2006. The Shahab-3A with either a 1,000 kg or 1,200 kg warhead, as well as the smaller, 800 kg warhead on the Shahab-3B. Now thanks to other comments by Safavi during the interview, we know that the cluster warhead on the Shahab-3 has 1400 bomblets. This is in turn indicates that bomblet weight is somewhere between .42 kg - .64 kg – either equal to, or slightly greater to the “RAND model” bomblets of .45 kg each.

(note that the -3A designations “-3A-1” and “-3A-2” are not official designations in any form, but are added for clarity in this report to allow for the two different reported weights for the -3A)

Unitary Warhead: 1,000 kg
Cluster Warhead: 1,400, .53 kg bomblets
(Google Earth)

Unitary Warhead: 1,200 kg
Cluster Warhead: 1,400, .64 kg bomblets 
(Google Earth)

Shahab-3BUnitary Warhead: 800 kg
Cluster Warhead: 1,400, .42 kg bomblets

The slightly heavier and lighter bomblets of course produce a different lethal radii then the .45 kg ones. While I'm not aware of any specific rule for scaling explosives at this level, the same equation used for scaling the unitary warheads above essentially describes what is happening here, but on a larger scale. Let's hope it fits!

This means that the warhead on the -3A can carry 1400 .53 kg bomblets and the -3B can carry 1400 .42 kg bomblets. Due to the scaling involved with the bomblets lethal radius and their corresponding known spread, we can ascertain that the threatened area for the -3A and -3B are 537 m and 425 m respectively.

RAND Model Bomblet - .45 kg
Lethal Radius: 6.09 m
Threatened Area: 116.74 sqm

Shahab-3A-1 Bomblet - .53 kg
Lethal Radius: 6.40 m
Threatened Area: 128.71 sqm

Shahab-3A-2 Bomblet - .64 kg
Lethal Radius: 6.83 m
Threatened Area: 146.79 sqm

Shahab-3B Bomblet - .42 kg
Lethal Radius: 5.92 m
Threatened Area: 110.43 sqm

Scaling things up to full scale, this means that each missile would have the following specifications:

Unitary Lethal Radius: 79.33 m
Unitary Threatened Area: 19,775 sqm
Cluster Spread: 240 m
Cluster Threatened Area: 180,194 sqm
Percent Change: 911%

Unitary Lethal Radius: 84.31 m
Unitary Threatened Area: 22,331 sqm
Cluster Spread: 256 m
Cluster Threatened Area: 205,506 sqm
Percent Change: 920%

Unitary Lethal Radius: 73.65 m
Unitary Threatened Area:17,042 sqm
Cluster Spread: 222 m
Cluster Threatened Area: 154,602 sqm
Percent Change: 907%

Unfortunately, what isn't known is the CEP of the missile. Safavi asserts that the accuracy is to within “30 m” which, if true, represents a monumental leap in accuracy for Iran. That being said, it remains unlikely as it is simply “too good”. Other estimates range from 250 m to 1,000 m. Of course, what also matters is range at which it is launched at. A missile launched close to the coast with only 100+ km to it's target would behave very differently from a Shahab-3 launched at Israel (or other target at the very edge of it's range)

Unfortunately, this section will have to remain blank for the time, which means that a comprehensive review is not possible.

It's also worth mentioning that Ballistic missiles behave differently from conventional artillery rockets because of the way they fly. The release of bomblets from a BM may require a whole set of different conditions, however, these are also unknown, so shall be ignored for the time being. 

Saturday, January 15, 2011

Larak Island

Larak Island

One of the eastern-most Islands in the Persian Gulf, Larak Island served as a major oil-export hub during the Iran-Iraq war (which interestingly enough, now appears to lack any major oil infrastructure). During the war, it was also rumored to host HY-2 AShMs.(1)

Today, limited imagery is available from Google Earth (December, 2002), but some scars of war are still visible, giving a hint of what the island might look like today.

The thin white lines that snake the island are roads. 

***Click to Enlarge***

Ringing the southern half of the Island are a series of light fortifications built alongside the coastline, consisting of berms and limited fighting positions, possibly with small pillboxes/bunkers in the same style as Sirri (2) Individual positions are hard to distinguish from many other common geological and man-made features (such as back-fill piles, land-clearance and other otherwise innocuous objects) alongside the coast.

An example of a common style includes the presence of two circular fighting-position of AAA gun pads set slightly behind the sand berm, and then accompanied by a handful of what could be other smaller buildings or pillboxes.

The most visible features on the island are no doubt the trio of firing positions found facing the south toward the shipping lanes, the likely stationing point for HY-2s during the war. They don't appear to be maintained to a high degree of readiness, but remember this was in 2002 before the shift to asymmetric warfare as a keystone strategy and the fact that these sites don't need to be kept immaculate in order to function.

The sites themselves consist of three 'prongs', each with three revetments, one large central node (L: ~23 m W: ~10 m) flanked on the shoulders by two smaller nodes (L: ~10 m W: ~5 m). Exact setups or configurations for specific missiles remain unknown, but it is possible for the smaller shoulder revetments to house the operators and supplies (such as trucks) while the central node is for a towed or self-propelled  launcher such as those seen with the HY-2. Radar's are typically separate vehicles, though newer launchers have integrated surface-search radars (TELAR). That being said, these sites configuration are most likely generic and do not necessarily indicate a specific type of missile used on Larak, or a specific configuration of launchers/radars/other equipment.

Along the northern side of the island, there are similar revetments; they are unlikely to be AShM launching zones because they face south, looking directly into hills and small mountains, making any apparent launch profile impossible. Other explanations include SAMs, artillery (such as on other islands), or equipment storage. The artillery option is possibly the least unlikely, but that's all can be said with such limited information. 

Raised on some of the small hills alongside the south/south-eastern side of the island are several lookout points consisting of small buildings. The western-most post is the largest and measures 16 m x 11 m and appears to be multi-storied. Of note is the large broadcast antenna located on the eastern side of the building. The eastern post on the other hand is only slightly developed and only what might be a bunker or earth-sheltered building can be observed. May be related to general watch-keeping, or may be closely linked with the islands anti-ship capabilities.

Further up the coast and a little more inland are another set of building perched upon a hill. Exact purpose is unknown, but the site also have a large broadcast antenna whose shadow can be seen on top of one of the buildings.

1) Wikipedia - Larak Island
2) Google Earth Community - "Sirri Refinery Complex" By: JSmithbitter 
3) Wikimapia