April 1914. After Britain’s declaration of war with Germany in August 1914, Kerr wrote to the head of the submarine service hoping for a return to an active role in the Royal Navy. In September he was told to report to HMS Vulcan, the submarine depot ship in Leith. Kerr hoped to be given command of a submarine but came to realise that the issue of his eyesight weakness precluded this. He made enquiries at the Admiralty about other opportunities and was offered the job as Rear Admiral Troubridge's flag lieutenant during a military mission to Serbia. He accepted and was given the rank of Lieutenant-Commander. Serbia As a consequence of the assassination of Archduke Franz Ferdinand of Austria in 1914, the Austrian government declared war on Serbia on 28 July of the same year. Their forces were initially repelled by the Serbian army and a standoff developed across the rivers Danube and Sava. Russia, France and Britain allied themselves with the Serbians and sent in small detachments to provide support. To restrict the movement of Austrian warships on the Danube and Sava the British deployed mines and installed static torpedo tubes on the banks of the rivers. Rear Admiral Troubridge, commanding a small force with eight 4.7 inch guns on Scott Carriages and a 56 ft picket boat, deployed to the front line. The guns were divided into four batteries of two guns with a Serbian artillery officer in command of each. Men from the Royal Navy and Royal Marine Artillery operated the guns; they were supported by as many as ninety Serbians, many of whom were responsible for the oxen used to move the guns. The picket boat had been transported overland from Salonika on the railroad, requiring some ingenuity to overcome various logistic difficulties. It was fitted with two cradles, one per side, to hold torpedoes that could be lowered into the water if and when required. On the nights of 22 and 23 April 1915 Kerr was using the picket boat to reconnoitre the reaches of the Danube west of Zemun. He was instructed by Troubridge not to endanger the craft. Eventually the crew spotted the silhouette of the Austrian monitors. As they approached they were challenged by a lookout and Kerr immediately ordered the first torpedo to be fired. This dramatically affected the trim the picket boat which swung off course. Corrective action was taken