[Goose]

S-400's in Sevastopol will not prevent use of low altitude SU25s or helicopters, though could limit use of Bakraktars flying at higher altitude. Even these may be low enough to stay out of range of missile defenses so far away (I'm not certain of their usual operating altitude).

The 9M96E family will do just fine destroying low altitude targets at a range of up to 120 km. The majority of the S-400 family missiles are semi-active radar homing (SARAH) missiles, but the 9M96E series is designed to be "fire and forget". This feature allows these missiles to be fired at targets that the launcher (and/or it's associated acquisition radar) cannot see. The A-50 Mainstay is supposedly capable of doing exactly that, although AFAIK we have never seen it do so. Something new may be learned. The 120 km range does limit the reach of these missiles. While the original purpose of these missiles was to defend Sevastopol, they are scattered all over Crimea and are mobile enough to pose a serious problem. They can reach most of the Kherson Oblast that way. The second issue is that flying an SU-25 at very low altitude from it's base to the target area and back is often difficult and accident-prone. Transiting part way at higher altitude is desirable, and that can be hard to do under the circumstances.

Ukraine will undoubtedly find a way. It just may not be cost-free. If it turns out the A-50 actually can't take control of the battle space then it is just Tors, Panstirs and MANPADS to worry about. That said, without acquisition help Tors and Panstirs are not that lethal against low flying aircraft. Their firing window is pretty small, but if you blunder into it you are in trouble.

And Russia will also need to take care not to shoot down their own planes. Here we can see their air defense take out one of their own Su34s. Oops!

https://twitter.com/GirkinGirkin/status/...P4RLTyyiYg

Aftermath-

https://twitter.com/GirkinGirkin/status/...P4RLTyyiYg

This was an interesting article about what a Kherson counter offensive may look like.

https://kyivindependent.com/national/wha...-look-like

It seems just recently a Russian SU-35 in the Kherson region was shot down by friendly fire.  I wonder if we are seeing secondary effects of HIMARS, where they are trying to shoot down HIMARS missiles, but accidentally targeting their own aircraft.

Could be. The Russian systems all have IFF on the launchers, but the missiles themselves do not. If the missile is SARAH the guys who launched it should detect the "friendly" in the area and not allow the missile to kill it. If it is active radar homing or infrared homing that is often impossible. It is possible the Russian aircraft did not have working IFF or that they didn't have the correct codes. Lots can go wrong in that arena. It is also possible the guys who launched the missiles violated the rules and did not de-conflict the targets properly.

It is also possible the Ukrainians did it, as I think they are claiming?

---

Can you provide more info on the basis for believing that attacking supply lines or air defenses in Crimea constitutes a "red line" for Russia?  That may be the case, but the information I read in the press does not seem helpful in reaching any such conclusions.

No, I can't, thus my question. Crimea is certainly a different case in that Russia has officially absorbed it. What that actually means is the issue.

I'm not confident that there is a "red line" where anything on one side will draw no significant response and anything on the other side will draw an escalation to mutually assured destruction.  Putin does not seem fully rational, so maybe ignore logic, but, to my mind, if he were rational, I would expect escalations commensurate with acts that the US takes.

Fine, but what actions can Putin take that would be "proportional"? He is already using missiles with over 300 km range in Ukraine. Unclear to me what "makes sense" as escalation. I think he might ignore attacks in Crimea unless or until it looks like Ukraine is going to actually invade it. Then Putin must do "something" (or quit).

 I suppose Putin might treat an attack on a bridge in the Black Sea as the same as an attack on civilian population centers like St. Petersburg, but that is not at all self-evident to me.

Nor to me. There is some evidence Ukraine has already staged limited attacks on "Russia proper" with helicopters. This was sort was ignored/swept under the rug. However, the Kerch Bridge is a symbol of Russia's "reconquest" of Crimea. It was a big deal when built and supplies an essential rail link to Crimea. It was also clearly built by Russia and was not there in 2014. Destroying it has both great practical and (even more so) symbolic importance. I don't see how Putin can ignore that if it happens. He will do something, I have no idea what.

[Goose]

S-400's in Sevastopol will not prevent use of low altitude SU25s or helicopters, though could limit use of Bakraktars flying at higher altitude. Even these may be low enough to stay out of range of missile defenses so far away (I'm not certain of their usual operating altitude).

The 9M96E family will do just fine destroying low altitude targets at a range of up to 120 km. The majority of the S-400 family missiles are semi-active radar homing (SARAH) missiles, but the 9M96E series is designed to be "fire and forget". This feature allows these missiles to be fired at targets that the launcher (and/or it's associated acquisition radar) cannot see. The A-50 Mainstay is supposedly capable of doing exactly that, although AFAIK we have never seen it do so. Something new may be learned. The 120 km range does limit the reach of these missiles. While the original purpose of these missiles was to defend Sevastopol, they are scattered all over Crimea and are mobile enough to pose a serious problem. They can reach most of the Kherson Oblast that way. The second issue is that flying an SU-25 at very low altitude from it's base to the target area and back is often difficult and accident-prone. Transiting part way at higher altitude is desirable, and that can be hard to do under the circumstances.

Ukraine will undoubtedly find a way. It just may not be cost-free. If it turns out the A-50 actually can't take control of the battle space then it is just Tors, Panstirs and MANPADS to worry about. That said, without acquisition help Tors and Panstirs are not that lethal against low flying aircraft. Their firing window is pretty small, but if you blunder into it you are in trouble.

And Russia will also need to take care not to shoot down their own planes. Here we can see their air defense take out one of their own Su34s. Oops!

https://twitter.com/GirkinGirkin/status/...P4RLTyyiYg

Aftermath-

https://twitter.com/GirkinGirkin/status/...P4RLTyyiYg

This was an interesting article about what a Kherson counter offensive may look like.

https://kyivindependent.com/national/wha...-look-like

It seems just recently a Russian SU-35 in the Kherson region was shot down by friendly fire.  I wonder if we are seeing secondary effects of HIMARS, where they are trying to shoot down HIMARS missiles, but accidentally targeting their own aircraft.

Could be. The Russian systems all have IFF on the launchers, but the missiles themselves do not. If the missile is SARAH the guys who launched it should detect the "friendly" in the area and not allow the missile to kill it. If it is active radar homing or infrared homing that is often impossible. It is possible the Russian aircraft did not have working IFF or that they didn't have the correct codes. Lots can go wrong in that arena. It is also possible the guys who launched the missiles violated the rules and did not de-conflict the targets properly.

It is also possible the Ukrainians did it, as I think they are claiming?

---

Can you provide more info on the basis for believing that attacking supply lines or air defenses in Crimea constitutes a "red line" for Russia?  That may be the case, but the information I read in the press does not seem helpful in reaching any such conclusions.

No, I can't, thus my question. Crimea is certainly a different case in that Russia has officially absorbed it. What that actually means is the issue.

I'm not confident that there is a "red line" where anything on one side will draw no significant response and anything on the other side will draw an escalation to mutually assured destruction.  Putin does not seem fully rational, so maybe ignore logic, but, to my mind, if he were rational, I would expect escalations commensurate with acts that the US takes.

Fine, but what actions can Putin take that would be "proportional"? He is already using missiles with over 300 km range in Ukraine. Unclear to me what "makes sense" as escalation. I think he might ignore attacks in Crimea unless or until it looks like Ukraine is going to actually invade it. Then Putin must do "something" (or quit).

 I suppose Putin might treat an attack on a bridge in the Black Sea as the same as an attack on civilian population centers like St. Petersburg, but that is not at all self-evident to me.

Nor to me. There is some evidence Ukraine has already staged limited attacks on "Russia proper" with helicopters. This was sort was ignored/swept under the rug. However, the Kerch Bridge is a symbol of Russia's "reconquest" of Crimea. It was a big deal when built and supplies an essential rail link to Crimea. It was also clearly built by Russia and was not there in 2014. Destroying it has both great practical and (even more so) symbolic importance. I don't see how Putin can ignore that if it happens. He will do something, I have no idea what.