Complex sentence: During this period, their engines were stopped to preserve fuel, but after the threat of British submarines increased, they kept steam up in their engines to preserve their ability to take evasive action; the steamer was moored in front of the battleships as a floating.
Split into simpler sentences: During this period, their engines were stopped to preserve fuel, but after the threat of British submarines increased, they kept steam up in their engines to preserve their ability to take evasive action. Additionally, the steamer was moored in front of the battleships as a floating.