The plane was delivering supplies to Poland and to Warsaw Uprising as well as to all the countries the flags are painted on the fuselage. As far as I understand, the Division 301 was also known as British 1585 Squadron and it was renamed by the Poles in 1944, from 'Pomeranian' (Ziemi Pomorskiej) to 'Warsaw Defenders Division' 'Warszawski'. 

Division 301

Lieutenant pilot Mieczysław Stachiewicz in the cabin of Liberator.

Division 301 'Ziemi Pomorskiej'.

Lieutenant pilot Karol Rach, on the right, and Lieutenant navigator Jan Paradysz in front of Mosquito FB VI. Beginning of the year 1944.