I didn't comment on the latest conflict between the US and Iran last week for two reasons. First, it broke out on Saturday, and that didn't leave me a lot of time to write something up. Second, in that time, the fog of war was still pretty dense, and I didn't see anything I could say where I would add value above and beyond what you'd get following the news.
But that changed pretty dramatically on Wednesday, when the Pentagon announced that an Iranian frigate had been sunk by a US attack submarine, revealed on Friday to be USS Charlotte, one of old Los Angeles class boats.1 This is only the second time in the history of the nuclear submarine that torpedoes have been used in anger, and the first in over 40 years, since HMS Conqueror put General Belgrano on the bottom of the Atlantic. Even better, we have video of the torpedo hit, and I thought there was enough interesting stuff going on there that it was worth dedicating this week's post.
Dena commissioning
So, first, what do we know about the victim? Dena was a unit of the Moudge class light frigates, domestically produced in Iran. These are definitely on the small side for frigates, with an official displacement of only 1,500 tons, and other sources given even lower numbers. Armament is a 76 mm and 40 mm gun, some lighter weapons, plus four SAMs that are about the size of SM-2MR and that look to have performance somewhere between that missile and ESSM, depending on variant. I can't quite see the logic of fitting such a small number of SAMs instead of a larger number of smaller missiles, and I wonder if they might be intended to be used in surface-to-surface mode. Rounding things out are a quartet of C-802 anti-ship missiles and a deck for an ASW helicopter, although there's no hangar and none of the pictures show the ship with the helicopter aboard, which makes me suspect that it's primarily intended for rearming and refueling helicopters based ashore. I also question the official speed of 30 kts, which seems a bit high for 20,000 shp on the claimed displacement. CMO gives 28 kts, which is more plausible.
The view from Charlotte before the torpedo hit
But none of this mattered on Wednesday. Dena was returning from the Milan naval exercise and an international fleet review hosted by India. This was all near Visakhapatnam, halfway up the east coast of India, and as Dena was headed home, Charlotte found her, and fired the fatal shot somewhere between 19 and 50 nautical miles2 off of Galle, on the southwestern tip of Sri Lanka. Initially, General Caine, the chairman of the JCS, reported that a single Mk 48 was used, but the same report that named Charlotte also claimed that the first torpedo fired malfunctioned, and the second was successful. Reports are that Dena was able to get off a distress call before she sank, although I suspect this is more likely to have been a self-contained, automated system given the damage apparent in the video. Ultimately, the Sri Lankans were able to recover 32 survivors and 87 bodies. Reports vary on how many were aboard the ship, and thus how many remain unaccounted for, with the total aboard reported as being between 130 and 180 depending on the source. I suspect the numbers towards the higher end are correct due to the relatively high ratio of bodies to survivors. The lower numbers imply that two-thirds of the crew either were killed in a way that their bodies ended up floating separately from the ship (a likely fate for anyone in the structurally destroyed aft section, but unlikely further forward) or died after successfully escaping the ship (somewhat unlikely given the relatively prompt arrival of rescue forces, although we still don't have a detailed timeline for that).
Which brings us to the video, which I've embedded here. The first thing to note is that this is clearly a thermal image, with the bright spot amidships being the funnel and the exhaust gasses from the diesels. Second, this is clearly a classic underbottom explosion, with the astonishing violence that usually accompanies those. The Mk 48 torpedo is designed to kill far larger ships, so it's not surprising how much damage we see here. What is slightly surprising is how far aft the torpedo detonates. Based on the stadiometer markings, the torpedo went off only 40' or so from the stern, and I would expect based on the other example I've seen of a Mk 48 hitting a surface ship that it would be aiming more amidships. In any case, you can see the structure of the aft hull coming apart as the bubble jet forms, as in the top image, exhaust gasses being driven out of the funnel by the inrushing wave of water and the main radar falling off the mast. Moments later, the lifting of the aft hull drives the bow down, and then things go entirely gray as the spray from the hit blocks out most of the image. By the time things clear, towards the very end of the clip and about 14 seconds after the torpedo hits, she almost looks back to normal, although this is obviously not true. There's no exhaust gasses, although the funnel itself remains hot, and it looks like there might be a gap in the hull just aft showing warmer interior spaces (probably some part of engineering). Whatever was on the flight deck is totally gone, and it's obvious that she's going down by the stern very quickly thereafter. Reporting is that she sank only 2-3 minutes after the hit.
The bow is driven down, and the spray column obscures the stern
Dena was not the only ship the Iranians had in the area, and on Thursday, the replenishment ship Bushehr was interned by Sri Lanka, while LST Lavan was interned by the Indians.3 The fact that there isn't a declared war going on makes things a bit confusing, but in practice, this means that the ship (and probably the crew) are effectively under arrest, taken off the board until the end of hostilities, but still belong to Iran. It was not unusual during the world wars for ships that would clearly be unable to reach a friendly port to seek internment in a neutral power, as it saves lives (and ships) relative to making the enemy actually sink them. This would have been a good plan for Dena, and it's not clear if the Iranians decided against doing so, or were unable to get India or Sri Lanka to agree to it before Charlotte caught up to her.
I'm going to avoid getting too deep into the legal weeds on the actual sinking, largely because that ties deeply into the legal status of US actions against Iran, something well outside the scope of this blog. All I can say is that in practical terms, Dena was clearly a danger to any non-submerged American forces in the region, and removing that kind of threat is generally considered to be well within the rights of a belligerent.
The end of the video, with the ship looking almost intact
But there's a last naval aspect to the conflict that eclipses all of this, the Strait of Hormuz at the mouth of the Arabian Gulf. Something like 20% of the world's supply of oil and natural gas passes through Hormuz, and it's always been Iran's trump card if they think there's an existential threat to the regime. They finally declared it closed a few days ago, and daily transit volume has fallen from the typical rate of about 120 ships a day down to single digits. At the moment, this looks to be largely downstream of insurance shenanigans, and we don't seem to have seen attacks on the few ships which have transited. The problem is that while the Iranian Navy looks to have been comprehensively smashed, it doesn't take a navy to close a 20-mile wide strait. Iran has a lot of options for nastiness, ranging from Shaheds to C-802s to unmanned surface vessels (which have already been deployed against tankers inside the Gulf) to mines. Mines are a particular concern, given the generally low state of USN mine warfare capabilities and the difficulty of clearing them while under missile attack. The price of oil is headed upwards, and the Gulf States are likely to become pretty unhappy with the war if the closure persists. Definitely an area to keep an eye on.
3/9 Update: Two interesting aspects have come out in the day since I've published this. First, Iran apparently requested docking permission for all three ships from India when the shooting started on the 28th, and India agreed on the 1st, three days before the sinking. It's possible that there was ongoing diplomatic wrangling about the details of the deal (the Indians wanted full internment, the Iranians were hoping to keep the ships on the board) but in any case, Dena could have been safe well before she was sunk.
Second, the Iranians are claiming that Dena was unarmed, and that this was obvious because she was on her way back from an exercise with India, because you have to be unarmed to participate in those kind of things. Now, from a strict law of war perspective, this is meaningless. There's a deck gun visible in the video, and that's more than enough to make her a legitimate target. "I am out of ammo" is easy to say and hard to check, and the laws of war are pragmatic about such things. I also find it highly doubtful on a practical level. I've never heard of this rule, nor had a former naval officer I contacted, and there's no trace of it on the internet before the past week. I also really doubt that the USN would be willing to offload 80 missiles from the destroyer scheduled to participate, both from a logistics perspective and because they generally try not to sail defenseless warships around. The Indians themselves are not willing to back up the claim that Dena was entirely unarmed, either. Maybe she was carrying a lighter load than usual, but that's the sort of thing which is very difficult to confirm without putting people onboard, and when combined with Iran's behavior re internment, leaves this firmly in "good shoot" territory.
1 Two things worth noting here. First, the Australians have confirmed that three of their personnel were onboard, presumably as part of AUKUS. Second, I correctly predicted that the firing submarine was an LA or Seawolf from the released video, which seemed quite a bit shakier than I would expect from the photonics mast on a Virginia. ⇑
2 A lot of sources seem to have standardized on 19 nm, but this is a recent development, and I'm not sure that this is correct. The continental shelf is unusually narrow in this area, barely reaching out to the 12-mile limit. ⇑
3 Interestingly, while Dena was several years younger than the blog, both of these ships were originally built for the Shah's government. ⇑
Comments
"in practice, this means that the ship (and probably the crew) are effectively under arrest, taken off the board until the end of hostilities, but still belong to Iran. It was not unusual during the world wars for ships that would clearly be unable to reach a friendly port to seek internment in a neutral power, as it saves lives (and ships) relative to making the enemy actually sink them."
Considering the widely-noted link between poor countries, even democracies, and police corruption/brutality, I wonder if interned sailors in poor neutral powers during the World Wars were treated much better than the neutral power's own citizens under arrest. Presumably they had every incentive to obey the Geneva Conventions and all laws of war.
Legally, interned personnel must be treated at least as well as POWs would. In practice, they can be treated quite a bit better (for instance, Swedish treatment of allied internees in WWII), and I would expect that most neutrals would do their best to treat internees fairly well for diplomatic reasons. In this case, it's not clear exactly what their legal status is, and the US has been putting pressure on India and Sri Lanka not to repatriate them. Haven't heard what the outcome there is.
Can you clarify the phrase "relatively high ratio of bodies to survivors"? I'm not at all well-versed, but I'm surprised anyone survived given the violence of that explosion.
Basically, they found almost three times as many bodies as survivors. I find this weird because I would expect a fair number of people to be unable to get clear of the ship before she went down, and almost nobody to die between going in the water and getting rescued. (I assume the Iranians have some reasonable life-saving equipment and this is the Indian Ocean, so hypothermia probably isn't killing people very quickly.) Most injuries that would stop someone from getting to a lifeboat/raft/debris seem like they'd also stop you from getting off the ship in the first place, and then your body isn't recovered.
That said, I'm not surprised we saw survivors. Probably nobody from aft, but I'd expect a lot of people in the forward half to survive the initial blast.
Oh, boh, are we having another Torpedo Crisis?
Two Mk48s launched, and a dud...
Does anyone know what Sri-lankan ship and/or ships went out to pick up the surviving crew and bodies from the INS Dena?
Surprisingly no where seems to say which ship did it.
It'd be ironic if it was one of the ex-USCG ships Sri-Lanka has.
I did not run across that information while I was looking into this.
"plus four SAMs that are about the size of SM-2MR and that look to have performance somewhere between that missile and ESSM, depending on variant. I can’t quite see the logic of fitting such a small number of SAMs" maybe wanting something with a longer range than ESSM or it was intended as an offensive ground to air missile? Not sure how good domestic or Chinese/Russian equivalents to the SM-2MR & ESSM are.
Regarding the number of bodies, I'm not sure where I read it (Instapundit or maybe Rantburg), but there were rumors of a dispute between small number of the crew and their captain and the captain kicked them off the vessel using the lifeboat. That MIGHT tie in with the reports that the USN warned the Dena twice to stop and surrender.
The only place I've seen that was the Daily Fail, and I don't take places which can't use a picture of the right submarine class very seriously.
"Definitely an area to keep an eye on." A lot of understatement there!
What do you think is the biggest risk to reopening without Iran's cooperation?
Presumably a convoy and air cover can stop most if not all the slower drones.
I don't have a good feel if we could have enough persistent surveillance and presence to stop small boats laying mines.
Then anti-ship missiles, whether conventional or ballistic, seem not fun to counter is such a constrained space.
If Iran decides to lay mines, we're in big trouble. Even if we get a good idea of where they are (and persistent surveillance is basically the whole point of the MQ-4C) clearing them is still going to be extremely difficult, particularly if it has to be done under fire. But so far, they seem quite content not to do that, because they are still exporting oil in their own tanker fleet, and we don't seem to have taken action against it.
The problem with other threats is mostly magazine depth. We saw in the Red Sea that we can counter pretty much any missile/drone they can throw at us, but that it gets expensive in terms of munitions very fast. Also worth noting that we'd probably need to convoy all the way up to Kuwait, and with maybe 16 Burkes in the region, we don't really have the forces to do that.
More broadly, I just found out that the torpedoing may be causing problems for merchant shipping by widening the area declared as a war zone. The premiums aren't what they are for a Hormuz transit, but it's an extra cost.
Thank you for this analysis!
Was there any obligation of US ships to offer aid to the survivors of the Dena?
It is my understanding that the submarine was the only US ship in the area. Submarines have not been expected to stop and render aid to merchant ships torpedoed (even by idiots who have no idea how a submarine works) since the early days of WWII, as radio allowed the sinking merchant ship to broadcast their position and request help.
I am not aware of any requirement for a submarine to stop and offer aid to any naval ship at any time.
I may be wrong about either or both of these.
@Belushi TD, Captain Todaro would not approve your attitude.
"What is slightly surprising is how far aft the torpedo detonates. Based on the stadiometer markings, the torpedo went off only 40′ or so from the stern, and I would expect based on the other example I’ve seen of a Mk 48 hitting a surface ship that it would be aiming more amidships."
Is it possible the torpedo was set to acoustic homing, and detonated directly beneath the propellers?
The Moudge class does not seem to be particularly lucky, with three of the six sinking or capsizing in the past decade, all before the USN became involved.
Seconding Onux's comments; Mk 48s have active/passive terminal homing, and that hit implies the stern was making A LOT of noise. Not sure what the exact machinery layout of the MOUJ-class is (Wiki lists her plant as two diesel mains and four diesel gens, but I can't imagine they are all that far aft, which implies either a bad prop or maybe a thrust bearing was bad?
Re: casualty numbers. Interesting comparison can be had with the sinking of ROKS CHEONAN (which many sources are ignoring in the list of "Ships sunk by submarines after WW2"); in that case, 46/104 personnel on board died (although with a messy political twist here, since most of the killed were draftees because that's where their berthing is).
I guess if you're running in full passive you might aim aft, I just sort of assumed that the Mk 48 was smarter than that. Didn't make much difference here, but might somewhere else. That said, not sure it would take a particularly bad prop to make that the main source of noise if Iranian acoustic design isn't particularly advanced.
I was extremely careful with my caveats, and specified "nuclear". Although that is a case which might bear looking into.
And, per wiki, 40 of the bodies were found when the ship was salvaged. Now, she didn't break in half for 5 minutes after the hit, which implies that the level of violence was a lot lower, but it does add support for my guess that there were more than 130 onboard.
"I guess if you’re running in full passive you might aim aft,"
If you are running in full passive mode you don't aim at anything - the torpedo will home in on the largest source of noise, which is likely to be the propellers either because of general principles, or especially if they have any slight damage or wear that causes extra turbulence or cavitation.
"I just sort of assumed that the Mk 48 was smarter than that."
Most people believe that it is smarter than that, particularly when running under control of a guidance wire or when using active sonar, but just because it can be smarter doesn't mean that it was used that way, versus a simpler passive homing mode. C.f. HMS Conqueror using an old WWII ear Mk8 torpedo to sink the Belgrano instead of the newer Tigerfish, because the older torpedo was considered more reliable. Also, there are the reports that two torpedos were fired by Charlotte, which suggests that the first missed or did not detonate. That might have caused the Captain to choose a simpler passive attack for the second.