Did WW2 airplanes ever jettison their empty external fuel tanks to act as weapons? Jettisoning an external fuel tank over a populated area is prohibited by the FAA as it will almost certainly cause injury and damage to the people in that area.
But did war airplanes during World War 2 ever use that fact to their advantage?
As an example, say a P-51 Mustang dropped its bombs onto a city/town as a part of its mission, and then they realize that their external fuel tanks are empty, and are ready to be jettisoned. Well, couldn't the P-51 just jettison the external fuel tanks over the city/town to cause some additional damage?
So, did war airplanes during World War 2 ever actually jettison their empty external fuel tanks over bombing targets to cause additional damage?
Yes, and not even empty tanks. It didn’t always work, but it’s happened:
     This is how American pilots used drop tanks as bombs during WWII.
Fun fact, cellulose drop tanks were developed to save metal during the war! The article references P-47s, but I would not be surprised if P-51s did the same.