After the action at Berzasca, Trapp had stationed some lighter units to keep tabs on the Allied fleet as a trip wire of sorts. The terrain within the Iron Gates was such that aerial reconnaissance was insufficient to ensure that unpleasant surprises would not occur. After constant campaigning, the light units anchored upstream from the defenses at Golubac, counting on the shore batteries to keep any Allied units from disturbing a well-earned rest.

Morning arrived with the pounding of guns as the Romanian fleet had managed to run the batteries unnoticed. Apparently, some enterprising Romanian civilians identified the Austro-Hungarian signals and passed them on to the Romanian fleet. The unit log of the westernmost shore battery noted "0130 six ships passed moving upstream. Recognition signals clear and bright." During the following inquest the officer in charge of the watch stated that the confusing situation along the Danube had left them unable to predict what would happen next. When unfamiliar boats arrived with the correct recognition signals it was assumed that the boats were Bulgarian and were the vanguard of a Bulgarian expeditionary force (a rumor making the rounds at that time despite the fact that Bulgaria had no Danube flotilla).

In recognition that the position taken by the officer was not a dereliction of duty but rather a terrible assumption, the expected verdict of the court martial was tempered to a reassignment to the Polish front.

Counters and maps from River Fleets may be used to play Blue Danube scenarios.