Complex sentence: The first was a surprise destroyer torpedo attack inside the harbor in early February 1904, this was quickly followed up with an attempt to block the harbor's entrance by sinking old steam ships (block ships) in the channel.
Split into simpler sentences: The first was a surprise destroyer torpedo attack inside the harbor in early February 1904. This was quickly followed up with an attempt to block the harbor's entrance by sinking old steam ships (block ships) in the channel.