On April 16 Moscow confirmed that its Black Sea flagship Moskva had sunk after the survivors of her crew of 500 men had abandoned ship. It is the biggest naval loss to enemy action since WWII and a major blow to Russia’s military prestige as it wages a destructive war against Ukraine. The tactically important Russian cruiser was hit by two Ukrainian-developed Neptune anti-ship missiles fired from land-based launchers near Odesa, whereas Moscow denies these reports and claims that Moskva was damaged by a fire and sank because her hull was breached by ammunition explosions it caused.

Details are still coming in but images released by Russia’s Ministry of Defence showing the crew receiving awards had only an estimated 250 sailors on parade, suggesting that 250 men were lost or injured. The ministry has released no casualty count and has suppressed information, telling family and friends of the sailors not to speak to the press or post on social media, according to reports.

The ship

Moskva was a formidable warship, designed in the 1960s and commissioned in 1982 as the lead ship of the Atlant Class. Her intended role was to deliver an overwhelming missile attack on a Nato carrier strike group with her 16 P500 Bazalt cruise missiles. In missile terms a P500 is a beast – a 5 tonne unmanned jet aircraft carrying a 1 tonne warhead (or a hydrogen bomb), with a range of 500 km. Launched with a solid-fuelled rocket booster, a salvo of Bazalts would fly to their target at some 2,000 km/h. On arrival the swarm of missiles would divide targets among themselves, four for the high value unit and the rest for her escorts, with the aim of saturating defensive systems. A single high explosive hit would disable an aircraft carrier or destroy a smaller ship, and the resulting fire would finish the job. A nuclear hit would tear a carrier apart. The P500 has since been upgraded to the P1000 – basically the same missile with a longer range and (probably) a better radar.

With the end of the Cold War the three ships of the class remained in service, as much for show as for war-fighting, though their Bazalt systems would certainly have given an opponent a tactical headache while they stayed afloat. The ships were allocated as flagships (a meaningless but flattering term) to the Black Sea, Pacific and Baltic Fleets, and spent their time showing the flag in their respective regions.

Moskva at war with Ukraine

In the context of the Ukraine war Moskva punched well below her 12,500 tonne weight. Her P1000 missiles are designed to attack ships, not land targets, and have no reported land-attack targeting system. Moskva’s only weapon system relevant to the support of land operations is a twin 130mm gun turret. The twin 130mm is a serious weapon – capable of throwing around a tonne of high explosive per minute in sustained fire out to a range of 25 km – but Moskva had only one mounting, and ammunition stowage for about five to seven minutes of fire at that rate.

At best Moskva could use her twin guns in the rear of a defending force to attack coastal targets, which are out of range of an attacking land force, or to give close fire support to an amphibious assault, and it is in that potential role that she offered the most significant kinetic threat to Ukraine. She appeared to be located where she was as a “poised” asset, to “pin” Ukrainian defensive forces in position in case an amphibious group appeared over the horizon.

Neptune ship-killing missiles

The Neptune missile belongs to a large family of subsonic ship-killers that are present in all the world’s major navies. The basic format is a 600-800kg missile about as long as a family car. The tail of the missile is fitted with a solid-fuelled rocket booster, which takes the missile off its launcher and up to its cruise speed within a couple of seconds. The booster is then jettisoned and a small air-breathing jet engine takes over to fly the missile at around 1,000 km/h, just below the speed of sound, to its target.

The physics of fuel load, fuel energy and engine efficiency mean that subsonic cruise missiles all share roughly the same range capability – 100-150 km when fired from sea level. If you drop your ship-killer from an aircraft at height you gain extra range as the missile converts height into distance flown, and if you lengthen the missile you get more fuel and more range, at the cost of size and therefore the number of missiles that can be fitted to a small ship.

A cruise missile will fly low for most of its flight – 50m above sea level – to take it away from turbulent, and therefore higher drag, air at sea level. As it approaches the radar coverage envelope of its target a sea-skimmer will drop down to 2-5m above sea level, depending on its setting, its technology and on sea conditions. At this height it can get much closer to its target before being detected. Generally a sea-skimmer will become visible to the target’s radar at about 22 km, with fifty seconds to run before impact.

In a rough sea state radar waves reflect off the sea surface and create a radar picture full of “clutter”. Clutter tends to concentrate near the emitter (where the angle of incidence is near vertical), but even at distance some clutter persists which might delay visual detection of the small echo of a sea-skimmer, especially by an inattentive or sleepy crewman. Modern radars exploit the Doppler effect to pick out a fast-moving body from background noise but Moskva’s 1960s radars are of the pre-Doppler generation. There are indications that the sea state on the night of the strike was rough, which would have helped delay detection.

Once the target is in visual range the sea-skimmer’s on-board targeting system kicks in, and this is where designers can add vital value. The basic targeting system is an active radar. However, radars can be jammed, spoofed (given false targets to lock onto) or seduced (when their target data is hacked). They can also be offered multiple radar targets using blooms of chaff (aluminium-coated clouds of microplastics), or can be blinded using chaff screens.

To overcome these countermeasures the designer can add passive radar homing (the missile detects the target’s radar emitters and homes in on them), optical homing (the missile uses a TV camera to see the target), infra-red homing (the missile homes in on the heat emitted by the target’s engine exhausts, or just the temperature difference between the steel target and the background sea), and even no homing at all (the missile measures target speed and course for a few seconds, predicts target position on impact and heads to that point without further guidance). This last is possible because it only takes a sea-skimmer fifty seconds to fly from the horizon to impact, and large ships are slow to turn or stop. The missile can also be designed to jump between targeting mode to react to or to anticipate the target’s defensive moves.

It can be seen that it can be relatively simple to manufacture a sea-skimmer (if you choose a simple terminal guidance system) or it can be highly complex (if you want to get clever with your terminal guidance). In either case missile weight is a governing factor – the more clever guidance the designer adds the more of the missile’s total weight is consumed by guidance systems, and the less weight is available for fuel (= range) and warhead (= lethality).

Most ship-killing sea-skimmers will deliver a 150kg warhead over a 150 km range at 1,000 km/h.

Ukraine’s Neptune missile is reputedly a development of the legacy Soviet KH35 KAYAK sea skimmer (Nato’s reporting name) developed by the Soviet Union from 1983. Neptune is at the larger end of the size range, with a launch weight of 870 kg. As most of the weight increase is fuel Neptune has a reported range of about 280 km, which gives it effective coverage of the Black Sea out to a line drawn from the tip of Crimea to the Romania/Turkey border. Neptune can be launched from a truck-based launcher. No information has been published on its guidance system.

Targeting Moskva

An average sea-skimmer has no effective capacity to loiter in an approximate target area and find its own targets, which means it must be aimed and fired at a very precise point in space. As it approaches that point it activates its seeker (whether active or passive) to localise the target within a narrow search arc of maybe seven degrees either side of its track. So a successful strike needs a very recent (within 20 minutes) and accurate (within a few miles) target position.

Traditionally a ship would obtain targeting data from a trailing submarine or from a trailing aircraft (perhaps her own embarked helicopter). Other sources of data can be a fix provided by triangulating radar or sound emissions from the target, or real-time satellite data where available.

Best of all (because it is most accurate and most timely) is a target fix provided from a radar-equipped aircraft flying at height over the battlespace. This was probably the source for the targeting data on this occasion.

Published flight records and tracks clearly show Nato AWACS aircraft flying circuits in Romanian airspace and on an east-west track in Turkish airspace over the Black Sea, more or less constantly since the start of the war. Moskva’s location has probably been precisely known at all times since these flights started (with identification provided by fingerprinting her radar emissions).

Fixing the position of the Moskva may also have been helped by other means, as according to reports Ukraine also launched a Bayraktar drone against the cruiser from the opposite direction, used to distract the crew and focus the more powerful of its two radar systems in the wrong direction. In addition to acting as a decoy, the drone would have also been able provide a precise location for the missiles.

Getting a hit

Returning to the moment when a Neptune missile appeared over the horizon at 22 km and with fifty seconds to impact, Moskva’s reaction would have been a combination of kinetic and electronic countermeasures. We’ve listed the possible electronic countermeasures (ECM) above. Moskva was old and probably had an out-dated ECM suite unable to jam a modern agile seeker jumping from active radar to passive radar and back at the speed of software. Neptune’s designers may well have had accurate information on Moskva’s ECM suite as well, gained during service in Soviet times.

Moskva is therefore more likely to have relied on attempts to shoot down the incoming missiles, with one or more of her three layers of hard-kill systems. The first layer is the pair of 130mm guns we mentioned earlier. Guided by radar these are theoretically capable of hitting an incoming missile, but only if they and their fire-control radars are at instant readiness and effectively operated.

The second defence layer is a suite of short-range agile surface-to-air missiles (Osa/SA-N-4 Gecko), of the same vintage as Moskva herself. SAN4 is command-guided, which limits the number of incoming targets that can be hit and puts a human decision-making step into its operation.

The third, and final, layer is a suite of six turrets fitted with 30mm Gatling-style guns capable of firing some 2,000 rounds per minute under radar guidance. The idea of these close-in weapon systems (CIWS) is to throw a wall of high explosives just in front of the sea-skimmer in the last five seconds of its flight, at 1,000 metres distance. The intention is to shred the missile before it hits.

These three layers combined give a reasonable probability of killing a single sea-skimmer, so long as all of their various radars, computers, launchers and turrets are available for instant reaction, and their operating personnel are in a permanent state of high alert – less likely in the middle of the night.

An attack which uses multiple sea-skimmers raises the chance of a hit exponentially. While the initial reports count two Neptune missiles fired, more recent, but unconfirmed, reports claim three Neptune missiles were used in the attack. Kyiv claims to have delivered such an attack on Moskva, with multiple missiles fired from two directions.

Hard-kill systems tend to focus on the lead missile, allowing the second, third or even fourth missile to slip past. Better still is to deliver a sea-skimmer attack with many missiles approaching from different directions. Attacked from two directions with multiple missiles the target’s physical assets are diluted, and its cognitive capabilities (crew attention) can also be overwhelmed. Modern warships allocate that kind of decision-making to an algorithm, but Moskva is the antithesis of a modern warship.

Geography makes Kyiv’s multiple missile claim entirely possible. Moskva was hit 120 km south-east of Odesa, and 120 km east of Primors'ke, near the Romanian border. With real-time location, course and speed data provided by a Nato AWACs it would have been an easy task to launch up to four Neptunes from one location and four from the other, timing the launches precisely to ensure that all missiles arrived at Moskva more or less simultaneously. We have no corroboration of how many Neptunes were fired, or from where, but even half that number would have a very high probability of overwhelming Moskva’s defences and countermeasures. Kyiv has claimed two hits.

A photograph of Moskva which emerged on social media last night removes any lingering doubt that this was indeed a missile strike.

When a sea-skimmer is hit by the inner layer of defence (those Gatling-style guns) it will disintegrate but not detonate. The missile fragments – 800 kg of fuselage, motor, fuel and explosive – fly on under momentum, and if the kill is close enough to the ship they will impact anyway with considerable kinetic energy, possibly sufficient to cause damage, penetrate the thin steel skin of the ship and to start the fires that the Russian side claim was the cause of the sinking of the Moskva.

The Ukrainian Neptune ship-killer is a 800 kg subsonic missile with a range of 150 km that carries a payload of 150 kg of high explosive.

Damage control

Neptune carries a 150 kg high-explosive warhead – about average for a sea-skimmer. Modern warships, even of 1980 vintage, carry little to no armour (except occasionally some around magazines), and a 150 kg explosion therefore does a large amount of damage, even to a 12,500 tonne ship.

If the missile has flown as designed it will strike two metres above the waterline and detonate deep inside the target rather than on her hull. The first effect is blast. 150 kg of high explosive will destroy everything within about 15 metres of the impact point (blast radius is reduced because the target is a honeycomb of steel compartments). The next impact is shock. Explosive shock is transmitted throughout the rigid structure of the target ship, throwing men violently around inside their compartments, breaking bones and causing concussion. Shock also dismounts equipment inside the ship (radar consoles, computers, radar transmitters, generators, switchboard equipment, ammunition hoists), will throw equipment off the upper decks into the sea, and turns any unattached equipment below decks into a missile. Finally, shock will disrupt any equipment that relies on precise alignment, like propeller shafts, fuel lines, high pressure air lines, ammunition hoists and so on.

After the shock comes fire. The warhead detonation sets alight anything combustible within its blast radius, while any unburnt fuel in the missile body adds to that fire. Fire in a warship is a particular challenge, because a ship has an abundant supply of combustible materials spread all over her interior (paint, wire insulation, hydraulic hoses, deck coverings, rubber seals on hatches and doors, diesel, ammunition, rocket fuel and a dozen other categories of combustibles). Added to that challenge is the fact that a ship fire must be fought in three dimensions – not just from each side but from above and below as well. And finally the high-pressure water mains used to bring water to the fire may themselves be damaged or destroyed by shock, and the machinery which powers them may well be damaged or destroyed.

The sum effect is that even a relatively small warhead presents an existential threat to a warship. If the resulting fire is not swiftly contained it quickly spreads (in three dimensions) consuming the very systems needed to fight it as it grows.

The target’s crew must not only fight the fire but also try to help injured personnel.

One result of a missile strike, which the crew rarely need to worry about, is sinking. Warships are built in a complex honeycomb of sealed compartments, and are generally designed to stay afloat even when many of these are flooded. A sea-skimming missile strike does little to damage a ship below her waterline, and after a missile hits ships tends to float quite happily. A hit ship is much more likely to burn out than to sink.

One hit can be fatal. Two hits in different parts of a ship present her crew with an almost insoluble fire-fighting problem. Water mains may be breached. The pumps, which provide pressure to those mains, run on electrical power and if a hit disables generators then electrical power may fail. Some 15% of the crew will probably be injured (mostly with bad burns and broken bones), demanding attention from the survivors. Two missiles mean two fires raging in different parts of the ship. As fires approach magazine spaces the risk that rocket propellant will catch fire increases. Meanwhile fires inside the ship heat deck surfaces to the point at which crew cannot walk on them, and then to a point at which decks deform and collapse underfoot.

None of this is theoretical. Last year saw a stunning example of how fire can destroy even a very large and modern ship when the 40,000 tonne USN amphibious assault ship Bonhomme Richard was set alight by a disgruntled crew member while alongside in San Diego harbour. The entire combined forces of the San Diego fire department, the ship’s own crew and all the available hands and equipment from every other US warship in San Diego at the time were unable to bring the fire under control. Bonhomme burned for ten days, only stopping when there was nothing left to burn, and has since been written off.

It can be seen how, after hits from just one or two 150 kg warheads, a crew might quickly need to abandon ship.

If a sea-skimmer will rarely sink a warship, the crew’s efforts at fire-fighting can do just that. If the fire is burning high up in the ship the water poured on to fight it can flow into natural traps inside the ship's internal compartments well above the waterline. A high-pressure hose pumps out many tonnes of water per minute. Panicked fire-fighting can therefore load a ship with hundreds of tonnes of water just where she doesn’t need it – high above her centre of gravity. In extreme cases fire-fighting water can completely destroy a ship’s stability and capsize her – which is almost exactly what happened to the 40,000 tonne Iranian ship Kharg in 2021, and what nearly happened to Bonhomme Richard.

As the few photos of the disabled Moskva show, she was listing when she was abandoned – a state consistent with the presence of a large quantity of fire-fighting water inboard. Moskva had also settled into the sea by approximately two metres. It is easy to calculate how much internal flooding is required to put her there - around 4,000 tonnes. With several fire hoses pumping three or four tonnes per minute each, a few hours of firefighting would deliver that quantity of water inboard. In the resulting state (called "loll" in ship stability parlance) even a very large ship will capsize. As the ship tilts under the weight of flooding a new problem arises – the small holes created by the initial missile penetration roll underwater, and external flooding then destroys what is left of stability. This appears to be what happened to Moskva, and the photograph that has emerged shows her just before this critical point. In a state of loll, and with water flooding through the 0.3-square metre impact hole, Moskva would sink in a flat calm, and it appears that the sea state was indeed mild just before she sank.

Hit or miss

Naturally, Kyiv’s narrative of a highly successful Neptune attack is not the only story on offer. Moscow has claimed that Moskva caught fire for unstated reasons, that the fire threatened one of her magazines, and that her crew abandoned ship because of the threat of explosion.

Moscow's narrative is comprehensively rebutted by the photograph of Moskva sinking. It is true that warships do occasionally catch fire. They are filled with equipment and supplies designed to combust or detonate, and with systems operating at high temperatures and pressures. However, in practice, warship fires mostly start in galleys (chip pans overheating), during maintenance alongside (welding equipment left active) or in machinery spaces. The latter are always fitted with elaborate fire drenching systems based on gas suppression or water flood. Chip pan fires are practised for often, and have their own fire suppression systems. Maintenance is unlikely to be the cause of a fire at sea. Magazines and missile stowage compartments are rigidly segregated, tend to be situated low in a ship (and therefore below most fires) and are always fitted with dedicated fire suppression systems and water flood valves. It is almost inconceivable that a non-combat fire would grow out of control to the point at which abandoning ship was the only course of action available.

What we see in the photograph is a missile penetration hole roughly amidships on the port side, about 2 metres above the waterline. The internal impact point was probably a main machinery space. Above this point the superstructure is burning strongly with smoke flowing from all points (we can also see actual hotspots of fire within the smoke). More smoke is emerging from open portholes along the main deck. The P1000 missiles forward of the impact point are unharmed. Further corroboration of a successful strike is the fact that Moskva's radar masts and aerials have been dismounted – probably by shock from the explosion.

There is a second (more ambiguous) impact point low on Moskva's port quarter, just forward of the break of her main deck. Here there is less evidence of uncontrolled fire, and it is possible that this missile (perhaps one of those fired from the western launch point) failed to detonate. However, on the hangar roof the two large fire hoses (installed to fight helicopter fires on the flight deck aft) are still operating at full pressure.

Moskva's life rafts were fitted just above this impact point. All those on the port side have been launched. Each raft is usually designed to take 50-60 men (allowing the whole crew to fit into the rafts from just one side), and the fact that they are all launched corroborates the report that Moskva was abandoned.

Moscow has claimed that all of Moskva's crew are safe and well, but that is highly unlikely to be the case. A missile strike anywhere within the main body of a warship is likely to kill the nearest 20 men, and injure another 40. Here we seem to have two strikes. The only published information on the Moskva's ship's company was Russian Ministry of Defence images of the crew on parade, where only about 250 sailors were present according to estimates, including the Captain Anton Kuprin, who was earlier reported dead, suggesting the remaining 250 sailors were either killed, missing or injured. An uncorroborated Turkish report suggests that 50 men have been recovered by a Turkish warship, which would be consistent with a single life raft.

Ukrainian Presidential Adviser Oleksiy Arestovych appeared surprisingly unsure of the cause of the explosion. “I don’t really have real information about this, and I prefer to wait and check quietly what sources say,” he said in an interview on CNN.

Implications for the war, and sea power in the Black Sea

Assuming the Moskva was indeed hit and sunk by Neptunes (and no other interpretation is now credible), what implications are there for the future conduct of the war?

First, Russia would have to accept that any ship sailing within about 280 km of Ukrainian-held coast is at serious risk of attack. That applies to amphibious assault ships, as well as to much smaller fast attack ships and ships equipped with Kalibr land attack missiles. Smaller ships are harder to hit – the target area is smaller, they are more agile, which means they can reduce hit probability by turning end-on to an incoming missile, they have more modern radars and close-in weapon systems, and being smaller are likely to attract smaller salvoes, but in spite of all that it seems likely that the Russian Navy will position its assets at much greater distances from the coast of Ukraine, reducing the number of frequently-used Kalibr cruise missile launch platforms available to Russian commanders for targets in western Ukraine and also reducing their reach.

In terms of amphibious operations, Neptune’s success substantially decreases the risks of an amphibious landing near Odesa. With targeting provided by Nato AWACs assets, an amphibious group would have to spend some seven to ten hours within range of a Neptune strike before reaching the beach – likely to be a suicidal exercise.

If it wanted to carry out an amphibious assault on or near Odesa Moscow would now have to invest considerable time and resources in hunting down and destroying Neptune launchers. Since these are essentially large trucks they may be hard to find.

The Neptune strike on Moskva therefore largely neutralises the amphibious threat to Odesa. That may release some number of Ukrainian troops for use on another front. We do not know what, if any, plans Moscow actually has for an offensive on the Odesa front. If the Russian troops on that front (who have been strikingly inactive for the past month) are there simply to pin and distract Ukrainian forces from joining other fronts then the removal of the amphibious threat may also render that “poised threat” empty, allowing the redeployment of larger numbers of Ukrainian units.

On the other hand, the strike does nothing to relieve the effective blockade of Ukraine by Russian naval forces. As Turkey has closed the Bosphorus straits to military traffic Moskva cannot be replaced, but it was only one Russian naval asset among many already in the Black Sea.

Russia still has a handful of helicopter-capable frigates on hand (helicopters are the most useful tool for boarding recalcitrant merchant ships to compel their compliance without bloodshed) but will regret the loss of Moskva’s pair of helicopters and additional presence. So the blockade of Ukraine will persist, at a greater distance from Odesa, but nevertheless will be effective.

In the arena of surface warfare and sea surface control Moskva was an imposing asset with long arms and heavy fists, but without any real surface threat to counter. Calls from Kyiv to deploy Nato warships into the Black Sea have consistently been ignored, partly from a reluctance to risk direct confrontation with Russia, partly because of the tight restrictions imposed by the Montreux Convention on entry to the Black Sea and partly because of Moskva’s potent ship-killing potential.

If, at some future point, Nato states become willing to confront Russia directly, and if Turkey allows Nato to ignore the limits of the Convention, then Moskva’s absence from the order of battle will lower the barrier to entry.

One state, of course, is not constrained by the Montreux Convention. Turkey, a member of Nato (if semi-attached) is at present adopting a neutral stance in the Ukraine war. The presence of Moskva and her sixteen P1000s may have been one factor in that choice. Her absence may slightly lower the barrier to a future decision by Turkey to support Ukraine with armed force.

So, if Moskva’s neutralisation has marginally changed the balance of naval power in the Black Sea, it is not likely to cause Moscow any real worry.

However, the reputational and emotional effect of Moskva’s loss is likely to be much more powerful. For Kyiv the sinking of the Moskva is, if nothing else, a huge propaganda coup and will considerably boost morale. The Moskva was the ship that hailed and ordered the Ukrainian defenders of Snake Island to surrender, eliciting the now famous response: “Russian warship: go f**k yourself.” Only days before the Moskva’s sinking the Ukrainian post office issued a stamp commemorating that exchange, that features a Ukrainian soldier on the shore flipping the bird to Moskva at sea.