In Roy Palmers book 'Folk Songs Collected by Ralph Vaughan Williams' (Dent, 1983) he includes a version of Child 287:'Captain Ward and the Rainbow' ('Ward the Pirate') collected by RVW from James Carter, a King's Lynn fisherman, in 1905.

Palmer relates that John Ward was an English seaman and mutineer who, in the early 17th century, travelled to Tunis,"turned Turk" and became a pirate in the Mediterranean (I presume that he would have been classed as a Barbary Corsair). He had some success in this enterprise, at one point seizing a Venetian galeasse worth two million ducats (a fabulous sum in today's money). He died in 1622 of the plague.

In 1628 the British Crown sent a warship, under the command of a Captain Rainsborrow/Rainsborough, to sort out the Barbary Corsairs who had been harrying the sea-lanes around Malta.

According to Palmer the earliest known version of 'Captain Ward and the Rainbow' is on a late 17th century broadside and he speculates that some "landlubber of a ballad writer" confused these two stories.

So this is another ballad that it is highly likely to have had its origins in the broadside press but passed into oral tradition and eventually ended up in the repertoire of a Norfolk fisherman.