Complex sentence: After the fall of Poland, the Royal Navy was strengthened by the arrival of two Polish submarines Orzeł (Eagle) and Wilk (Wolf) and the formation of Polish Navy in the United Kingdom then supplemented with leased British ships.
Split into simpler sentences: After the fall of Poland, the Royal Navy was strengthened by the arrival of two Polish submarines Orzeł (Eagle) and Wilk (Wolf). The Polish Navy in the United Kingdom was then supplemented with leased British ships.