Complex sentence: Union mortar boats, led by Commander David D. Porter had for four days been attacking Fort St. Philip and the nearby Fort Jackson and the "Louisiana" was brought to the location in hopes of aiding the resistance to Porter's attacks.
Split into simpler sentences: Union mortar boats, led by Commander David D. Porter had for four days been attacking Fort St. Philip and the nearby Fort Jackson. The "Louisiana" was brought to the location in hopes of aiding the resistance to Porter's attacks.