Ukraine has arranged with its partners that it will be receiving warships to ensure the safety of ships in the grain corridor in the Black Sea.
Source: President Volodymyr Zelenskyy, in response to questions from Ukrainska Pravda at the Grain From Ukraine conference in Kyiv on Saturday
I find it hard to believe that they will be receiving anyone larger than a glorified PT boat. Certainly nothing larger than a frigate.
Of which there are plenty of that class up and down the Danube.