Moscow's artillery has begun falling on cities that have anchored Ukraine's eastern defenses for over a decade — a campaign ISW warns could last years
Executive Summary
- Russia has begun artillery and drone preparation for a spring-summer 2026 offensive against Ukraine's "Fortress Belt" — the fortified cities of Kramatorsk, Sloviansk, Druzhkivka, and Kostyantynivka that have formed the backbone of Ukrainian defenses in Donetsk Oblast since 2014.
- For the first time in the war, Russian tube artillery struck Kramatorsk's suburbs on February 26-27, marking the operational shift from long-range harassment to close-range battlefield preparation.
- The offensive will likely be a multi-year campaign costing Russia catastrophic losses, but its success or failure will determine the political geography of any future peace settlement.
Chapter 1: The Fortress Belt — Ukraine's Last Line in Donetsk
The term "Fortress Belt" refers to a chain of heavily fortified Ukrainian cities running roughly north-south through central Donetsk Oblast: Kramatorsk, Sloviansk, Druzhkivka, Kostyantynivka, and Dobropillia. These cities were transformed into layered defensive positions beginning in 2014, when Russia first sent troops into the Donbas and fomented a separatist uprising.
For twelve years, these cities have served as Ukraine's operational center of gravity in the east. Kramatorsk houses the Ukrainian military's eastern command. Sloviansk — where the 2014 conflict began when Russian intelligence officer Igor Girkin seized government buildings — carries deep symbolic weight. Together, these cities form an interlocking defensive network connected by the H-20 highway, their industrial infrastructure repurposed into fortification systems that would require enormous firepower and manpower to crack.
After Russia's capture of Pokrovsk in late 2025, the Fortress Belt became the final major urban defensive line before the administrative boundary of Donetsk Oblast. Its fall would fulfill Russia's declared war aim of "liberating" the entire Donetsk region — a political objective that has driven Russian military strategy since 2022.
Chapter 2: The Preparation Phase — What ISW Detected
The Institute for the Study of War (ISW) assessment of February 27, 2026 identified several converging indicators that Russia has begun the preparatory phase of its offensive:
Artillery Preparation: Russian forces shelled Bilenke, a settlement roughly 14 kilometers from the frontline and immediately northeast of Kramatorsk, on February 26-27. This marked the first time Russian tube artillery — as opposed to longer-range missiles or glide bombs — struck Kramatorsk or its suburbs. Tube artillery engagement at this range signals the frontline has advanced close enough for direct battlefield preparation, a qualitative escalation from the previous pattern of standoff strikes.
Battlefield Air Interdiction (BAI): Russia has been conducting a systematic campaign to interdict Ukrainian logistics along the H-20 highway connecting the Fortress Belt cities. Geolocated footage from February 26 showed Russian drone strikes against a civilian cyclist on the H-20 northwest of Kostyantynivka and against Ukrainian positions in Oleksiievo-Druzhkivka. Russian forces are deploying fiber-optic drones, "sleeper drones" that lie in ambush on roads, and tactical FPV strikes to deny Ukrainian vehicles the use of supply routes.
Force Buildup: A Ukrainian servicemember operating in the Sloviansk direction reported that Russian military command is deploying reinforcements to the area — a direct indicator that offensive operations are being prioritized.
White Phosphorus Use: Geolocated footage from February 27 confirmed Russian use of white phosphorus munitions against southwestern Kostyantynivka, followed immediately by a FAB-1500 guided glide bomb strike. Approximately 2,000 civilians remain in the city. This escalation in munition use reflects the brutalizing pattern Russia has followed before major offensives — Mariupol, Bakhmut, and Avdiivka all saw similar escalations.
Chapter 3: The BAI Revolution — Russia's New Way of War
Russia's Battlefield Air Interdiction campaign represents a significant evolution in how the Russian military fights. ISW's dedicated February 24 assessment documented how Russia has been improving the "intensity, tempo, precision, and depth" of its BAI campaign since late 2025.
The key innovation was Russia's integration of Starlink satellite terminals onto tactical and long-range drones in late 2025-early 2026. This connectivity extended FPV drone ranges dramatically, enabling Russian forces to strike Ukrainian supply lines and logistics up to 100 kilometers behind the frontline. In January 2026, Russian drone strikes hit sections of the E-50 highway — a major east-west artery — between Pokrovsk and Pavlohrad, roughly 78 kilometers from the front.
SpaceX's February 1 blocking of Starlink for Russian users in Ukraine degraded this capability significantly, but Russia has adapted. Russian forces are now using:
- Fiber-optic drones immune to electronic warfare jamming
- Mesh network communications that bypass satellite dependence
- Upgraded "mothership" drones that deploy smaller FPV munitions
- Modified glide bombs (KABs) with extended ranges
- "Human safari" tactics — persistent drone patrols hunting individual vehicles and personnel on roads
The effect has been to create increasingly isolated pockets along the Ukrainian frontline, stretching logistics chains and creating gaps that Russian infantry can exploit through infiltration tactics. This is the same operational pattern that enabled Russia's advance toward Pokrovsk in 2025.
| BAI Element | Capability | Range | Countermeasure Status |
|---|---|---|---|
| Fiber-optic FPV | Jam-proof precision strike | 10-20 km | Limited; physical interception required |
| Starlink-enabled FPV | Extended precision strike | 50-100 km | Degraded after Feb 1 SpaceX block |
| Mesh network drones | Semi-autonomous strike | 20-50 km | EW partially effective |
| KAB glide bombs | Heavy area strike | 40-70 km | Air defense, but supply limited |
| Sleeper drones | Road denial/ambush | Frontline to 20 km | Detection extremely difficult |
Chapter 4: The Manpower Equation
Russia faces a fundamental contradiction: its most ambitious offensive since the 2022 full-scale invasion comes at the precise moment its manpower pipeline is under the greatest strain.
ISW reported that in January 2026, Russia's casualty rate outpaced its recruitment rate for the first time since the start of the full-scale invasion. Russia suffered approximately 9,000 more casualties than it recruited — a structural deficit that cannot sustain a multi-year urban offensive campaign.
Moscow's response has been twofold:
University Recruitment: The Russian Ministry of Defense has expanded recruitment to at least 95 educational institutions, pressuring students through face-to-face meetings, propaganda film screenings, and a "carrot and stick" approach offering salaries, debt forgiveness, and education grants while threatening underperformers. Students are promised assignment to Unmanned Systems Forces units — lower-risk drone operations — but contracts often contain language allowing reassignment to any unit, including infantry.
Information Space Control: The Kremlin detained Readovka founder Alexey Kostylev on fraud charges — part of a broader campaign to co-opt or suppress pro-war media figures who cannot be fully controlled. ISW assesses this is conditioning for potential domestically unpopular measures such as involuntary reserve callups, which would be necessary to sustain a Fortress Belt campaign.
The historical parallel is instructive. Russia's assault on Bakhmut (2022-2023) cost an estimated 60,000-100,000 casualties for a city of comparable size to individual Fortress Belt cities. The Fortress Belt comprises four to five such cities in an integrated defensive network. Even with optimistic Russian assumptions, a campaign of this scale would likely require 200,000-400,000 additional casualties over 2-4 years — numbers that would demand either covert mobilization or fundamental changes to Russia's social contract.
Chapter 5: Scenario Analysis
Scenario A: Grinding Multi-Year Siege (45%)
Basis: This follows the Bakhmut/Avdiivka/Pokrovsk pattern — sequential city-by-city assaults using overwhelming firepower, human wave attacks, and gradual encirclement. Russia targets Kostyantynivka first (the southern tip, closest to current lines), then Druzhkivka, and eventually Kramatorsk-Sloviansk.
Historical precedent: Bakhmut took approximately 10 months and cost 60,000+ Russian casualties for a city with less sophisticated fortifications. Kramatorsk-Sloviansk have been fortified for 12 years.
Trigger: Current artillery preparation and BAI campaign continue through March-April; ground assault begins May-June 2026.
Timeline: 2-4 years for the full belt. Kostyantynivka potentially falls within 6-12 months; Kramatorsk-Sloviansk would take significantly longer.
Investment implications: Prolonged high-intensity conflict sustains defense spending and commodity demand. European defense stocks continue outperforming. Energy markets remain volatile on supply disruption risk.
Scenario B: Operational Failure and Stalemate (35%)
Basis: Russia lacks the concentrated force necessary for a decisive offensive against prepared urban defenses. The Starlink blocking has degraded BAI effectiveness. Ukraine's Coalition of the Willing allies provide sufficient ammunition and drone supplies to attrit Russian forces faster than they can replace losses. The January recruitment deficit persists and worsens.
Historical precedent: Russia's 2022 Kyiv offensive and the initial Sloviansk-Kramatorsk battles of 2014, where Ukrainian forces successfully defended both cities. Also the multiple failed Russian offensives in Zaporizhia Oblast in 2023.
Trigger: Russian ground assaults in April-June suffer casualty rates exceeding 1,000/day (the Bakhmut peak), forcing operational pauses. Ukrainian drone and artillery innovations neutralize Russian BAI advantages.
Timeline: Russian offensive culminates within 3-6 months without strategic gains.
Investment implications: Frozen conflict scenario becomes baseline. European defense budgets maintained but urgency declines. Commodity markets partially normalize. Peace negotiation pressure increases.
Scenario C: Escalatory Spiral — Russia Uses Unconventional Methods (20%)
Basis: Frustrated by conventional failure, Russia escalates to thermobaric weapons, expanded chemical weapons use (building on white phosphorus), or targets critical civilian infrastructure to force mass evacuation. The BAI campaign expands to hit the Fortress Belt cities themselves with sustained glide bomb campaigns similar to Mariupol 2022.
Historical precedent: Mariupol siege (2022) — Russia reduced the city to rubble over 3 months. Grozny (1994-95, 1999-2000) — complete urban destruction.
Trigger: Russian ground offensive stalls; Kremlin faces domestic pressure with approaching political events; escalation becomes the path of least resistance.
Timeline: Escalation within 3-6 months of offensive stall.
Investment implications: Major risk-off event. European defense spending accelerates further. Energy prices spike on broader conflict fears. Nuclear risk premium returns to markets.
Chapter 6: Investment Implications and Market Impact
Defense sector: European defense stocks (Rheinmetall, BAE Systems, Saab, Leonardo) remain the clearest beneficiaries. The Fortress Belt offensive guarantees sustained ammunition consumption — Ukraine fires an estimated 6,000-8,000 artillery rounds per day defending eastern positions. EU SAFE bonds and NATO 5% GDP targets provide demand visibility through 2030+.
Energy: The offensive itself has limited direct energy impact, but it unfolds against the backdrop of the Iran crisis and Hormuz blockade. Any escalation in Ukraine compounds global energy supply stress. European natural gas demand for military industrial production adds to TTF price floor.
Commodities: Copper, aluminum, and steel demand from defense production sustained. Titanium supply disruption risk if fighting damages Ukrainian mining infrastructure in Donetsk region.
Currency: Prolonged conflict supports dollar strength on safe-haven flows, but competes with ongoing de-dollarization trends. Euro benefits from defense spending as fiscal stimulus.
Ukrainian reconstruction: The longer the offensive lasts, the larger the eventual reconstruction bill. Current estimates exceed $800 billion. Early investors in reconstruction-linked instruments (Ukrainian sovereign debt, infrastructure funds) face binary risk.
Conclusion
The shelling of Bilenke on February 26-27 marked a quiet but significant threshold. For the first time, Russian tube artillery reached the suburbs of Kramatorsk — the heart of Ukraine's eastern command and the symbolic anchor of the Fortress Belt. What follows will be the most consequential military campaign since Russia's initial 2022 invasion.
Russia's chances of seizing the entire Fortress Belt within a militarily relevant timeframe are constrained by a manpower deficit, degraded BAI capabilities following the Starlink block, and the formidable twelve-year investment Ukraine has made in fortifying these cities. But Russia has repeatedly demonstrated willingness to absorb staggering losses in pursuit of political objectives — and the "liberation" of all Donetsk Oblast remains the Kremlin's non-negotiable war aim.
The Fortress Belt's fate will shape the terms of any future peace settlement. If these cities hold, Ukraine retains a powerful bargaining position. If they fall, the war's trajectory fundamentally shifts. Either way, the siege ahead will be measured in years, not months — and the human cost will be devastating.
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