How a Black Sea ceasefire would benefit Russia
The Memorandum | No. 12.2025
Ukraine and Russia are on the verge of agreeing to a ceasefire in the Black Sea. Some reporting seems to suggest that such a ceasefire has already been agreed, but overlooks the fact that the Kremlin stated an agreement would only come into force after a number of sanctions against its food and fertiliser trade, as well as banking, were lifted, which is yet to happen. Given these recent developments, it is prudent to ask how important the maritime domain is to the war in Ukraine, how the maritime campaign has developed since Russia’s full-scale invasion in February 2022, and which steps His Majesty’s (HM) Government should consider moving forwards.
Understandably, most attention during the fighting in Ukraine has been focused on the brutal trench warfare in the east of the country, and on the regular Russian missile and drone bombardments of Ukraine’s cities and energy infrastructure. As any military strategist will tell you, the decisive domain in conflict is almost always the land, but – and this is firmly the case in the fighting between Russia and Ukraine – the sea and air domains (as well as space and cyber) can wield a significant influence on events onshore and below the skies.
Both Russia and Ukraine are heavily reliant on maritime trade for their prosperity. Before the full-scale invasion, approximately 70% of Ukraine’s total exports, and crucially around 90% of Ukraine’s agricultural exports (roughly six million tonnes per month), transited through the Black Sea. Without Black Sea trade, the Ukrainian state would quickly come under severe financial pressure.
Russia is less reliant on the Black Sea, but it still plays a significant role in filling the Kremlin’s coffers. Around 7.5% of Russian liquified petroleum gas exports transit the Black Sea, as do almost the entirety of its grain exports. Since February 2022, both countries have taken action to bolster the capacity of other routes to mitigate the economic fallout from the naval campaign. For example, the European Union (EU) has so far spent billions of euros to help facilitate imports and exports to and from Ukraine over land. However, trade flows in a certain way for a reason, and it is difficult (and costly) to buck the market. This mutual dependence on maritime trade is one of the reasons why Moscow and Kyiv, for a time at least, came to an arrangement to allow both of them to continue exporting grain through the Black Sea.
If Russia were able to enforce control over the Black Sea, it would in effect be able to cripple Ukraine’s ability to self-sustain the fight on land. This is why, in the early months of the conflict, Russia’s Black Sea Fleet was highly active in closing off these maritime routes (alongside naval mining efforts) and launching missiles from the sea at targets onshore. However, the Ukrainians – supported by the weapons and knowhow of the Kremlin’s troublesome Anglo-Saxon adversary – mounted an impressive campaign of sea denial. Through the use of land-based anti-ship missiles, air-launched cruise missiles and long-range Uncrewed Surface Vessels (USVs), Ukraine was able to cause tremendous damage to the Russian Navy, aided in part by out-of-date Russian equipment and training.
Given that Moscow has already essentially written off the Black Sea theatre for the moment, a ceasefire is a bargaining chip which can be leveraged for gain without significant loss.
To date, 21 Russian ships and submarines have been destroyed and seven damaged, including the sinking of the fleet’s flagship, the guided missile cruiser Moskva. Although the Russian Navy has slowly adapted to the threats (there has not been a naval loss for some time now), it has been mostly confined to trying to survive in the eastern part of the Black Sea rather than being able to menace Ukraine in the western part. Given the failures of the Kremlin’s maritime campaign, a naval ceasefire of any kind in the Black Sea looks to benefit Russia significantly at this stage in the war.
Given that Moscow has already essentially written off the Black Sea theatre for the moment, a ceasefire is a bargaining chip which can be leveraged for gain without significant loss. As well as the benefits to Russia’s seaborne trade, a pause in conflict in the Black Sea offers the Russian Navy breathing room to fix up its remaining ships, perhaps even upgrading some of their capabilities, and bring in more uncrewed vessels.
Moreover, the Russians may try to persuade the Turkish government to lift its prohibition on warships transiting through the Dardanelles and Bosphorus (the Turkish Straits) under the Montreux Convention, arguing that a ceasefire means there are no longer ‘wartime’ conditions in place. This would open up the possibility of reinforcing the Black Sea Fleet with ships from Russia’s other fleets. It is also currently unclear how any ceasefire would be enforced, and what the penalties would be for it being broken – the deal has been negotiated by the Trump administration, but details from the White House are scant on the specifics.
If Russian ‘grey-zone’ activity in the Black Sea receives little pushback, this could easily embolden Russia to resume full hostilities.
There are two likely outcomes should an agreement materialise fully. In the first, Russia will leverage sanctions relief to agree to a ceasefire which it will adhere to while reconstituting the Black Sea Fleet. This creates the opportunity to break the ceasefire at the first militarily worthwhile opportunity – Moscow has a terrible record for keeping to its word – with no consequences which the Kremlin views as enough to stop such a course of action. In the second, Russia will use that same leverage and time but not overtly break the ceasefire, instead relying on its well-worn tactics of ‘grey-zone’ warfare and ‘accidental’ action to antagonise Kyiv and strangle the Ukrainian economy, pushing up to the line on what Ukraine’s supporters would consider unacceptable behaviour, while avoiding crossing it. If Russian ‘grey-zone’ activity in the Black Sea receives little pushback, this could easily embolden Russia to resume full hostilities.
Given Ukraine has, through military success, been able to keep a maritime corridor open along the western extremities of the Black Sea following Russia’s withdrawal from the ‘grain deal’, none of the potential outcomes from this ceasefire deal are particularly beneficial to Kyiv.
Even in the best-case scenario, Ukraine faces the likelihood of continuing Russian aggression in the Black Sea without being able to respond under American pressure, while Russia benefits from potential sanctions relief to replenish its coffers for further military investment.
HM Government should do what it can to help Ukraine by shaping the situation in three ways. Firstly, Britain should make clear to the United States that British and European sanctions on Russia will not be lifted as part of this deal, and make the argument that American sanctions should not be lifted either. Secondly, HM Government should do what it can to ensure that Ankara keeps the Turkish Straits closed so as to not permit the Russian fleet in the Black Sea to be reinforced. Finally – and most importantly – the United Kingdom must keep supplying Ukraine with what it needs to maintain sea denial – missiles, USVs, mine countermeasures, training and whatever else is required, in addition to continuing to explore fresh ways of putting pressure on the Kremlin to end its war of aggression. Ultimately, allowing Russia free rein in the maritime domain would be both outrageous and disastrous.
Dr Emma Salisbury is a Research Fellow in Sea Power at the Council on Geostrategy
William Freer is a Research Fellow in National Security at the Council on Geostrategy
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