Complex sentence: M'Namara gave chase and after a pursuit lasting six hours overhauled and captured what turned out to be the "Aimable Theresa", armed with two brass howitzers and 18 men.
Split into simpler sentences: M'Namara gave chase and after a pursuit lasting six hours overhauled and captured her. She was found to be the "Aimable Theresa", armed with two brass howitzers and 18 men.