This is the ship that the author Joseph Conrad sailed on wasn't it? There's an account called 'At Sea with Joseph Conrad' by J.G. Sutherland in which he describes the ship. It's really a lovely, and short read. Very interesting, and you can find it online if you type in the title. The last chapter says that this ship, the HM Brigantine 'Ready,' engaged two u-boats on June 16th, 1917 off the coast of Brittany, sinking one. The result; awarding of two Distinguished Service Crosses and three distinguished service medals to commander and crew. Perhaps this is the ship you are referring too? It was a small sailing vessel outfitted with guns but flying neutral colors. It's first tour occurred under Sutherland in oct-nov of 1916.