'Uncle Sam' was a German and Italian special forces operation on the Cassino front in Italy to interrupt Allied supply movements (20/21 May 1944).

Since May 1944 a German sabotage group had been operational in Naples, the Allies' primary supply base in Italy. From mid-May this group worked in close co-operation with Italian Fascist resistance fighters. On 20/21 May, one element of the combined German and Italian sabotage group organised a group of three frogmen to attach limpet mines to six large freighters in the harbour of Naples. At the same time another team of the German/Italian sabotage group prepared to sabotage the Allied petrol pipeline extending from Naples toward the front. The results of these Axis undertakings remain moot.