Ukrainian commander asks for international help to evacuate from Mariupol 1:02
(CNN) --
The second phase of Russia's invasion of Ukraine, an offensive in the eastern Donbas region, has already begun.
The question is whether it will be more successful and competent than the first phase, and whether Ukraine will have enough troops and weapons to prevent or even block it.
Russian Foreign Minister Sergei Lavrov said on Tuesday that the operation in Donbas is "a very important moment of this whole special operation."
Russia's goal is clear and has been publicly stated: to secure all of Ukraine's eastern Donetsk and Luhansk regions, parts of which have been controlled by Russian-backed separatists since 2014. A second goal is to crush the remaining resistance in the port city of Mariupol to consolidate a land bridge linking Russia's Rostov region with Crimea, which Russia seized from Ukraine eight years ago.
To this end, the Russian forces that were deployed to the north and east of Kyiv were redeployed and, in some cases, reconstituted after suffering heavy losses.
Armored vehicles from the so-called Donetsk People's Republic drive down a street in Mariupol on April 18.
Now these vehicles, and other newer units, are entering Ukraine from the northeast.
US officials estimate that Russia has mobilized some 78 tactical groups in eastern Ukraine, probably numbering 75,000 troops, and more are being assembled in Russian border regions.
So far, their tactics have been straight out of the Russian playbook: massive use of artillery, rocket and missile systems followed by advancing armor.
Luhansk towns such as Severodonetsk, Popasna and Rubizhne have been reduced to rubble, with electricity, gas and water supplies destroyed.
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But Russian progress on the ground has been modest.
This may be because they have not taken the time to regroup after the defeat they received in February and March.
The United States believes that Russia is learning from failures in northern Ukraine and applying the lessons in Donbas.
The Institute for the Study of War (ISW) states that "Russian forces did not take the operational pause that was likely necessary to properly reconstitute and integrate damaged units withdrawn from northeastern Ukraine into operations in the east of the country."
US officials estimate that Russia has lost up to 25% of its pre-invasion combat firepower.
fencing Donbas
CNN's analysis of satellite images, dozens of social media videos and statements from both sides suggest the Russians are now trying to advance on three axes.
Imagine the Donbas as a square: Russian forces are already on three sides, leaving only the west open for the Ukrainians to receive reinforcements and, if necessary, retreat.
From the south and east, forward Russian units have advanced, at best, a few kilometers this month.
In the south they had already advanced, taking territory from the Zaporizhia region, neighboring Donetsk.
This week, they have started shelling villages inside Zaporizhia.
From the north there has been little progress after taking the city of Izium earlier this month.
What is unclear at this point is whether the Russians are able and willing to shift gears, and whether a better coordinated offensive is just around the corner.
The balance of the Kyiv campaign suggests otherwise, but US officials believe that for now Russia is still carrying out "shaping operations ... to make sure they have logistics and support in place."
Still, the ISW assesses that "the Russian military is unlikely to have addressed the root causes that made previous offensives difficult: poor coordination, inability to conduct cross-country operations, and low morale."
An elderly man walks past an unexploded tail section of a 300mm rocket embedded in the ground in Lisychansk, Luhansk region, on April 11.
Ukrainian tactics
The Ukrainians have proven to be astute strategists in this conflict, ceding territory to preserve resources and using their knowledge of the terrain and mobility to inflict losses on Russian units.
This week, Ukrainian soldiers emerged from the town of Kreminna in the Luhansk region where they were outgunned.
Now they must decide if they want to mount a static defense, which could lead to units being destroyed or surrounded by Russian artillery, rockets and armored tanks.
The alternative is mobile defense, that is, fight and withdraw from less vital terrain, hit the Russians as they fall back, and then hold their lines on terrain of their choice.
At the same time, the Ukrainians will try to disrupt Russian supply lines, sowing confusion and challenging Russian logistics and morale.
And the morale of some Russian units, deployed for their second offensive in a few months, may be fragile.
Pro-Russian Donetsk People's Republic militia soldiers walk past damaged vehicles during heavy fighting in an area held by separatist forces in Mariupol.
One of the Russian targets is the city of Sloviansk, but the surrounding territory includes forests, rivers and swamps, which are difficult to navigate and require specialized bridging equipment.
When the Russians are confined to the roads, as became clear north of Kyiv, they are more vulnerable to both Ukrainian drones and light anti-tank missiles.
The Ukrainians are not limited to playing defense either;
in recent days, small units have made modest advances east and south of Kharkiv, potentially threatening Russian supply lines.
If they can keep this up, the Russians would have to dedicate units to guard these lines.
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There are already signs that Ukraine's special forces are operating behind Russian lines: A road bridge on a main entry route from Russia was blown up last week.
Unexplained damage also occurred to a railway bridge inside Russia, outside Belgorod.
The Russian Army relies on rail for much of its logistics.
In this aspect of the battle, the support of Western intelligence services can play a critical role.
Another important aspect of the coming struggle is cultural.
Ukrainian units enjoy a certain autonomy and are encouraged to exploit opportunities that arise on the battlefield.
Even in the absence of clear direction or orders, they have the motivation to fight.
In contrast, the Russian chain of command is rigid and the culture does not encourage taking the initiative.
Still, Ukrainians also face considerable risks.
They are basically fighting inside a box that could be closed if the Russians were successful in one or more directions.
They will have to maneuver intelligently, as they did around Kyiv, always alert to the risk of being surrounded.
Local civilians walk past a destroyed tank during heavy fighting in Mariupol on April 19.
When Mariupol falls, the Russians will be able to redirect the forces that were engaged in that assault, but have been degraded and depleted by nearly two months of urban combat.
Above all, in a race against time, Ukraine needs a constant replenishment of weapons and ammunition, much of which must now come from outside the country through a long supply line vulnerable to interception.
They need more anti-tank weapons and mobile air defenses.
Counterattacks to disrupt the Russian offensive would have to be protected from the air.
On Tuesday, a senior US official said Washington was working "around the clock" to get weapons into Ukraine at an "unprecedented" speed.
The United States has already authorized $2.3 billion in arms and equipment shipments to Ukraine since the invasion.
"What is unprecedented here is the number of successive withdrawals that we are moving at this speed," the official said.
The goal is Victory Day
There has been talk that the Kremlin wants to make tangible progress by May 9, the date on which Russia celebrates Victory Day, marking Nazi Germany's defeat in World War II.
At the current rate of progress, that seems unlikely.
The bigger question is whether this conflict will drag on into the summer, in a grim war of attrition.
The Russian military would have to rotate units, drawing on its limited reserves, to maintain a conflict that has already hit its ground forces.
His calculus (and the Kremlin's political strategy) will be affected by the effectiveness of the Ukrainian resistance and the ability of Western governments to supply Ukraine with more and better equipment.
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In "War on the Rocks," Jack Watling of the Royal United Services Institute in London says: "Ukraine's defiance has bought him time and an opportunity not only to prevent further Russian advances in Donbas, but also to shape to the battle beyond it. If Ukraine's allies act today, they can deter or at least prepare an offensive for the summer."
Resupply is urgent.
The Biden administration last week authorized another $800 million security package, which included artillery and anti-artillery radar.
On Tuesday, the president indicated that more packages are expected.
Ukraine will need offensive equipment if it wants to take advantage of any vulnerabilities in the Russian lines, and that includes heavy artillery (such as battle-ready tanks) as well as a host of other systems.
Watling says there is no time to waste.
"Providing Ukraine with tactical mobile air defense systems like the National would allow Ukraine to maneuver close to the Russian border and retake cities while assaulting Russian supply lines."
The National, or NASAMS, is an advanced, mobile surface-to-air missile system.
Western governments understand that this is a critical moment: raising the cost of Russia's "special military operation" to the point where it is unaffordable.
The Ukrainians are crying out for more and better weapons, especially as they try to keep their air force in the air.
Still outnumbered and outgunned, they will need agility, determination and reinforcements to hold off the second phase of Vladimir Putin's war against Ukraine.
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