Sorry for being so clueless, but what "lead" are they going to heave? A piece of heavy metal used for bullets and read as if written "led" or something else read as if written "leed"?

(Granted, it should probably rhyme with the "Diamond Head", but since I've heard "Peterhead" sung as "Peterheed" in "The Bonny Ship the Diamond" this ain't helping much. Couldn't find this verse on YouTube, either. Help me, Mudcat, you're my only hope.)