Under the command of Lieutenant Hendrikus Goossens, "Zwaardvisch" moved to Rothesay the following month and began sea trials based out of Holy Loch until February 1944. Throughout late February and into March, the submarine undertook patrols into the Atlantic and then off the coast of Norway. Later, she attempted to find the before returning to Dundee. A patrol to the Portuguese coast followed in May, after which she put into Gibraltar, where orders transferring the vessel to the Far East were received. Arriving in Trincomalee, Ceylon, in July 1944, "Zwaardvisch" came under the operational control of the British Far East Fleet, and conducted a patrol through the Strait of Malacca, during which time she attacked several ships, including "Kim Hup Soen" and two Malaysian sailing vessels, mainly with her deck gun.