Sentence:  None of us were more than shaken by the blast; we pulled ourselves together, and I laid and fired again. And that went better, for I holed her on the <WSD>water line</WSD> and that shell burst inside. 
Meaning of the word marked with <WSD> tags:  Any one of several lines marked upon the outside of a vessel, corresponding with the surface of the water when she is afloat on an even keel. The lowest line indicates the vessel's proper submergence when not loaded, and is called the light water line; the highest, called the load water line, indicates her proper submergence when loaded.