On 3 September 1916, the Danish steamer SS Johan Siem was stopped off Newhaven by a German submarine, with the steamer's crew abandoning ship, but TB 5 came up from Newhaven with two trawlers and drove the submarine off and took Johan Siem into Newhaven. On 3 May 1917 the German submarine UB-40 torpedoed and sank the merchant ship SS Clodmore off Newhaven. TB 5 rescued the crew of Clodmore. On 6 June 1917 TB 5 spotted what appeared to be the conning tower of a submarine which dived away. TB 5 attacked with four depth charges bringing up a thick oil slick over a considerable area. The success of the attack was subsequently judged by Naval Intelligence as "Improbable".
