# What does it take to sink the Russian cruiser Moskva?

On April the 14th, 2022 the pride of the Russian Black Fleet, the Slava class cruiser Moskva sank after allegedly being hit by two Ukrainian made cruise missiles, according to the official Ukrainian and American statements. Needless to say, this was one of the most significant surprises of the war in Ukraine. A ship of that size and capability was not supposed to have been sunk that easily, so the mainstream thinking went. I will analyse in this article whether such prejudice was justified and how exactly could the Ukrainians have sunk the ship with merely two missiles.

## Slava class cruisers

Moskva was a guided missile cruiser of Slava class built in the late 70s and commissioned in 1982. Ships of this class are 186 meters long and have a full load displacement of 11,500 metric tons. This makes them larger than the USN Ticonderoga class cruiser, but smaller than PLAN’s Type 055 Renhai class cruisers. The primary role of Slava class cruisers was anti-shipping against US carrier battle groups. Armed with 16 P-500 Bazalt missiles with a range of 550km and a massive 1000kg warhead or a 350kt nuclear warhead they presented a formidable threat at the time they entered service.

Their secondary role was fleet air defence. Equipped with the S-300F Fort system, consisting of 64 long range SAMs (93km) they protected the fleet from aircraft and missile. For additional protection of the ship itself, a layered air defence setup was implemented in form of 2 SA-N-4b Gecko short range SAM systems (12km) and an impressive 6 30mm CIWS guns.

The S-300F relies on the Top Dome as its fire control radar. Top Dome uses a 4m diameter radome fixed in elevation but trainable in azimuth. This is an electronically scanned radar operating in X-band, with a reflector type phased array. A limitation is that the ship has only one such radar and its coverage is less than half of a hemisphere. It is commonly assumed that the radar can engage three targets simultaneously with 6 missiles. However, a reputable authority like Norman Friedman1 claimed that it can control up to 12 missiles in flight against 6 targets, time sharing between target and missile tracking.

According to speculation from a Japanese blogger, the Top Dome may in fact be a dual band transmissive/reflective phased array with two RF feeds, as depicted in this illustration:

Personally, I find this dubious as for this to work there would have to be two phased arrays back-to-back, one reflective and one transparent.

For short range defence, the ship employs two SA-N-4b Gecko systems. In this system, the acquisition radar is collocated with the target and missile trackers. The director controls two missiles simultaneously against a single target using command guidance. Missiles are loaded onto a double arm launcher for a high rate of fire. This system was specifically designed to counter low flying sea skimming anti-ship missiles.

## Attackplatforms

According to the report from the US and Ukraine, 2 Neptune anti-ship missiles were fired at the Moskva cruiser and both scored a hit. The ship sank in the hours following the impact after suffering an extensive fire and flooding.

The R-360 Neptune is a relatively small anti-ship missile with a range of 300km and a 150kg warhead, roughly comparable to the French Exocet in destructive power4. It is based on the Soviet Kh-35 anti-ship missiles with improved range and electronics. It has an active radar seeker that activates approximately 20km from the target. After locking on the target, the missile descends to approximately 2-5 meters.

Target acquisition appears to be provided via the Ukrainian made Mineral-U over-the-horizon radar. In passive mode, the radar can detect and classify targets at up to 600km. In active mode, it can detect destroyer sized targets at ranges of at least 250km.

## Attack circumstances

According to H I Sutton writing for Naval News, the cruiser was spotted 50 nm off Ukrainian coast close to the time of the attack:

“A ship matching Moskva’s size and situation is seen at 45°10’43.39″N, 30°55’30.54″E. This position is [30 nm] east of Snake Island, 80 nautical miles from Odesa and 50 nautical miles from the Ukrainian coast. The satellite passed at 6.52pm local time. Based on analysis by multiple people, we are confident that this shows Moskva’s final hours.” Source: https://www.navalnews.com/naval-news/2022/04/satellite-image-pinpoints-russian-cruiser-moskva-as-she-burned/

Now, there is still a lot of speculation regarding how exactly the targeting data was provided to the shooting platform(s). One possibility mentioned earlier, is that the Ukrainians used the Mineral-U radar to detect, track and establish a firing solution on Moskva.

Another hypothesis is that Moskva was tracked by TB-2 drones which relayed its location to a ground station. Yet another hypothesis is that the targeting data was provided by one of the numerous NATO aircraft loitering in the theatre.

## Analysis

The analysis will be conducted with the assistance of the Command: Modern Operations commercial simulator. The data derived from this simulator is for illustrative purposes only. Do not take the information derived from the simulator as an accurate account of events.

The simulator does not yet have the Neptune missile in its database, therefore I will be using its closest analogue, the Kh-35 (SS-N-25) missile it is based on. According to the simulator’s database, the missile may perform a terminal pop up manoeuvre and slam into a ship’s deck from a high angle.

### Defences and Staying Power

Modern naval defence systems are quite effective against most forms of aerial attack. However, there is usually an upper limit in the number of missiles a ship can be expected to defend from. Because of that, it is held that defence at sea is tactically the weaker form of combat compared to defence on the ground3.

Defence systems are typically categorised into active and passive or hardkill and softkill, as depicted in the table below:

Staying power is a measure of how many missile hits it takes to achieve a mission kill on warship.

### Cube Root Rule anomaly

Within naval research, there is a famous counterintuitive empirical rule of ship survivability known as the Cube Root Rule. Lt Thomas Beal, USN, discovered that the bomb weight expressed in thousand-pound bomb equivalents (TPBE) required to put a ship out of action is roughly proportional to the cube root of the ship’s displacement expressed in thousands of tons. Therefore, if one TPBE can disable a 3,000 ton ship, two $(2 = \sqrt[3]{\frac{24,000}{3,000}})$ TPBE can disable a 24,000 ton ship.

To actually sink a warship required far more ordnance on target, particularly in terms of bombs:

It should be pointed out that the data above was sourced from WW2 records, when capital ships were much better protected than they are today. Separate studies on the effectiveness of anti-ship cruise missiles have produced similar estimates in terms of Exocet Missile Equivalents. For example, to sink a 3,000t ship it took on average 2.8 Exocet missiles2.

Based on the above cruise missile studies, it would take roughly $(4.38 = 2.8\cdot\sqrt[3]{11,500/3000})$ Exocet equivalent missile hits to sink the Moskva, on average. This demonstrates that modern warships are significantly more vulnerable to damage compared to their WW2 predecessors.

Note: Cpt. Cowden (ret) derived a slightly larger estimate of 4.64 Neptunes, rounded to 5. Source: https://www.realcleardefense.com/articles/2022/04/19/neptunes_the_moskva_and_how_not_to_sink_a_cruiser_827840.html

### Simulation

I will use multiple salvo size scenarios to simulate attacks against Moskva:

1. 8 Kh-35 missiles
2. 12 Kh-35 missiles
3. 16 Kh-35 missiles
4. 24 Kh-35 missiles

The missiles will be fired from beyond the horizon. Moskva will be in alert mode, with all its radars operating. Weather conditions will be set to fair. There will be no terrain within the radar horizon, as was the case according to open source intelligence.

As you can see in the image below, the incoming anti-ship missiles are detected at the extreme edge of the radar horizon, at about 17.5nm while flying at 30ft and 530 knots, first by the high mounted Top Steer (Frigate) radar and then by the Top Pair radar soon after.

Switching to the radar horizon view, we can see that the missiles were detected as soon as they crossed over the horizon edge.

In Command, the Top Dome FCR is modelled as capable of engaging up to six targets with six missiles simultaneously:

Even when the cruiser is engaged from the nearly opposite direction, the Top Dome FCR is still able to track and engage missiles from both sides. This might be an overly generous assumption on the part of the simulator, as most phased array radars suffer significant degradation to their performance beyond a 120 degree FOV.

Red lines denote radar illumination beams. Green lines denote radar tracking beams.

Summary of a 8 missile salvo attack:

Summary of a 12 missile salvo attack:

Summary of a 16 missile salvo attack:

Summary of 24 missile salvo attack:

### Compromised ship scenario

In this scenario, I disabled the long range Top Dome FCR radar. Therefore, the only remaining missile defence for the Moskva are the SA-N-4b Geckos.

Furthermore, I set the weather conditions to heavy rain, cloudy and sea state 4. I was not able to observe any impact on the performance of radar sensors: sea skimming missiles were still detected at the edge of the radar horizon and engaged with unchanged efficacy.

Furthermore, I set the crew training level to novice increasing the OODA (Observe, Orient, Decide, Act) loop to 10s. The simulator makes the assumption that the Moskva is a highly automated warship and even with an incompetent crew the computerised defence system will enable a relatively rapid reaction time. This is a highly debatable decision, in my opinion.

Summary of a 8 missile salvo attack:

Summary of a 12 missile salvo attack:

In one of the attacks with 12 missiles, there was 1 leaker that got through and struck the ship causing major flooding:

Summary of a 24 missile attack salvo. Finally, the Moskva was sunk! It took 5 hits to accomplish this, just as the above analysis had predicted:

### Surprise at EMCON

Another hypothesis is that Moskva may have been operating at EMCON (Emission Control) and was caught flat footed with all its radars down. To enhance the element of surprise I retained the heavy rain and low visibility weather conditions, together with the novice crew training level to prolong the reaction time.

As you can see in the image below, the cruise missiles were detected only at the moment their radar seekers turned on, just 4nm from the ship thanks to a very accurate firing solution:

This time around, Moskva managed to fire off a much smaller number of defensive ordnance and was struck with 3 missiles causing significant flooding and fire:

## Conclusion

No matter the number of missiles fired, an alert and nominally operating Moskva was able to shoot all of them down, without taking a single hit. Even splitting the cruise missiles to attack from opposite directions did not seem to change the balance.

Therefore, I explored two scenarios where the ship was in a compromised condition. In the first such scenario, I had the Top Dome FCR disabled and the crew training levels reduced to novice. Still, it took 24 simulated Neptune class missiles to sink the Moskva, after the ship took 5 hits.

In the second scenario, I had the ship operating at EMCON with all its radars deactivated. This time, with a much reduced reaction time even a salvo of 12 missiles was able to seriously damage the ship by scoring three direct hits.

Yet, according to the Ukrainian account, only 2 missiles were fired at the Moskva and not only did they both score a hit, but the ship went down with only 40% the ordnance that would normally be required to sink it. For this to be true, something must have been seriously wrong with the Moskva. Either its search or fire control radars were down or for some reason the crew failed catastrophically in their reaction to the attack and equally badly in the subsequent efforts at damage control.

Finally, there were some reports that during the attack, a major storm was active in the area. If the sea state was very high, this might have prevented the ship’s missile launchers from safely releasing their weapons and the CIWS guns from accurately tracking the incoming missiles.

## References

1. The Naval Institute Guide to World Naval Weapon Systems, 5th Edition; Norman Friedman; Naval Institute Press, 2006
2. Fleet Tactics and Naval Operations, 3rd Edition; Capt Wayne P. Hughes Jr. (USN) and RADM Robert P. Girrier (USN); Naval Institute Press, 2018
3. Fighting the Fleet: Operational Art and Modern Fleet Combat; Jeffrey R. Cares and Anthony Cowden; Naval Institute Press, 2021
4. https://missilethreat.csis.org/missile/exocet/