Complex sentence: With the Russian frigate Aurora present the allies continued a blockade of Petropavlovsk, and in late April 1855 the Russian Army abandoned Petropavlovsk, and in May a Royal Navy squadron took possession of the harbour.
Split into simpler sentences: With the Russian frigate Aurora present the allies continued a blockade of Petropavlovsk, and in late April 1855 the Russian Army abandoned Petropavlovsk. In May a Royal Navy squadron took possession of the harbour.