Being polemic doesn't help much either, don't you think?
I use "may" instead of "is" because there are very few informations on those days, available. I checked , and on April 17 there was an air raid ( South african aircrafts if I am not wrong), so the information may be accurate.
the Germans used those barges to defend the harbour and they became a very efficient method of persuasion whilst discussing the surrender when tito partisans invaded Trieste.
rgds