People have been predicting Ukraine has no chance at taking Crimea ever since it became apparent this war would last longer than a few days. Rarely do I see rationals as to why (cue long responses in the comment section) other than “it gets narrow”.
A narrow front can often be an advantage to a defender as it allows a smaller force to defend against a larger force because it makes it difficult for the larger force to bring its full power to the fight. There is a practical limit to the number of forces that can be stacked in a small area and continue to fight effectively. This is even more true when it comes to massing infantry in the faces of large volumes of artillery.
Further, because there is a limited set of options for the attacker to advance, fortifications become far more valuable and cost effective. When defending a large front, pouring concrete for a pillbox can be a lot of work for nothing if the enemy never comes close to that pillbox. In a narrow strip, you can pretty much guarantee it will see action, making the effort more valuable.
On the western side, the isthmus is roughly 10 miles long from Preobrazhenka to Krasnoperekopsk. It narrows to 5 miles wide near Preobrazhenka, widens out, and then splits into numerous strands with the widest being 2.5 miles near Krasnoperekopsk. 2.5 miles is not a lot of room to maneuver. On the eastern side the only connection is a bridge.
The viability of a Ukrainian attack to retake Crimea will clearly depend upon the condition of the forces involved and the circumstances in which it is started. I get the impression from those who say it is impossible as them imagining the full Russian army in peak form (did that ever exist?) lined up to defend one small piece of land. It won’t be. It also won’t be completely undefended. A battalion can commonly defend 3 km of frontage so Russia only needs a few BTGs to put up reasonable fight. But that’s at the isthmus. While a D-day level amphibious assault is clearly not going to happen, Ukraine can employ small unit attacks with US provided patrol boats and helicopters increasing the number of troops Russia needs to keep on Crimea’s shores.
At this point what Russian troops are present there are likely to be a mishmash of broken BTGs cobbled together on the fly. It will probably be of highly mixed quality. A lot will depend on whether Russia manages an organized retreat with much of its equipment, or whether it ends up a rout. As they only need one or two solid BTGs, let’s just assume they manage to keep 2 intact enough to put up a good fight.
So how does it proceed? Ukraine will continue to use HIMARs to obliterate any supply Russia has coming through. If the war has gone this far, the Kerch bridge is highly likely to be down or sufficiently damaged. Resupply will need to happen through ships that involve long, slow, unloads at piers. Considering Russia has already removed a significant portion of the Black Sea fleet from Sevastopol, we can surmise that Ukraine has the ability to interfere with resupply to some degree. A lot may depend on how many supplies can come in through the south east shore furthest away from Ukrainian missiles. The Sea of Azov will certainly be off limits to Russian ships due to missiles. Even if Ukraine can’t hit the ships or ports for whatever reason, it’s still many more miles of truck transport to the isthmus that Russia has shown to be very poor at. There are railroads on Crimea, but Russia will have the same problem it currently does of not being able to unload its trains close to the front due to the danger of HIMARS.
So the Russians will quickly find themselves in a place where they have had severe trouble again and again. They will be in poor supply and unable to get sufficient artillery rounds transported in to perform their standard doctrine of blow everything up in sight. Even if they have HIMARS resistant stockpiles in Sevastopol that’s still a long truck ride for the Russians. Perhaps they have hardened underground stockpiles of artillery shells prepared in Krasnoperekopsk? Enough to last them months? Does this level of planning and investment sound like the current Russian army to anyone?
I think it’s a fair bet HIMARS will continue its decimation of Russian supplies, particularly supply hungry artillery. Ukrainian M777s can then go to work on any functioning Russian guns. Ukrainian tanks can defeat any possible pillboxes. I’m sure the US Army will be sharing any fun breaching equipment they may need for other fortifications.
The thing is, a narrow isthmus doesn’t help nearly enough when the isthmus is only 10 miles deep and HIMARS can go 60 miles or more. Any Russian troops anywhere near the isthmus can be targeted with copious western weapon systems. Russia could pack 50 BTGs in there and that would only up the kill rate of Ukrainian shelling and further stress Russian logistics.
So can several BTGs hold a narrow strip of land indefinitely with poor supply under relentless shelling? Fortifications are helpful, but they are not magical. If Russia can’t keep its fleet safe in Sevastopol already and the Ukrainians aren’t even close to the isthmus, I don’t think they have a chance in hell of keeping Crimea. Yes that bit of frontage will cost more for Ukraine in lives than other frontage, but not an insurmountable amount. Taking Crimea is certainly doable if Ukraine has already beaten Russia back to the isthmus.