Complex sentence: One of these left Liverpool in July 1862 as a "merchant ship" and rendezvoused with supporting ships in the harbour of Praia da Vitoria, since Portugal was neutral and the Azores were far away from hunting US Navy ships.
Split into simpler sentences: One of these left Liverpool in July 1862 in the guise of a "merchant ship" and rendezvoused with supporting ships in the harbor of Praia da Vitoria. This meeting-place was chosen because Portugal was neutral and the Azores were far away from pursuing US Navy ships.