In WWII the OSS were contacted by the Norwegian underground, saying that the entire country's catch of sardines had been purchased by the Germans and was to be shipped to the German U-Boat bases in the country. They underground assumed that the sardines were going to be used to provision the U-boats, as a compact and high protein food supply. The underground said that they had access to the sardines and could put something in them if the OSS could provide it.
The OSS sent the Norwegians croton oil, which is a very powerful laxative. The effects of this on a U-boat crew can only be imagined. But they never found out whether the sardine sabotage worked..