 On 4 December , Warramunga and Bataan supported the emergency withdrawal of Allied troops from <unk> . Becher decided to sail up a channel of the Taedong River known as Short Cut , which according to his charts should have allowed him five to ten feet of clearance . The chart proved inaccurate , and Warramunga ran aground at 23 : 15 ; Becher 's only option was to wait for the rising tide to float the destroyer off . Warramunga came free at 23 : 50 without having sustained damage , and was able to resume her mission , escorting troop transports south . Later , Becher brought Warramunga alongside Bataan and entreated the latter 's commander , via megaphone , to keep quiet about the incident . With Becher 's promotion to captain due , he was concerned that if the Naval Board became aware of the grounding his promotion would be delayed until an investigation had taken place . His " well @-@ earned " rise in rank came through as scheduled on 31 December . On the journey south , Warramunga 's crew developed a new way of signalling between ships that was considerably quicker than using international code flags . Known to the crew as the " Murphy Method " , it involved wrapping messages around potatoes and throwing them from one ship to the other . 
