Another minelaying operation took place on 25–26 June; this time, "Thetis" escorted minelayers that laid a field in the Sea of Åland. "Thetis" again came under torpedo attack from an unknown submarine, though she was not hit. On 19 July, "Thetis" was based in Windau for a planned attack on the Gulf of Riga by elements of the High Seas Fleet. In August, "Thetis" was assigned to the fleet that was to break into the Gulf of Riga to support the German Army's attempt to capture the city. On 8 August, the Germans made their first attempt to force the Irben Strait, during which "Thetis" and the torpedo boat were damaged by mines. "Thetis" had to be towed back to Libau by minesweepers. The attack failed due to heavy Russian resistance, and the operation had to be postponed. In the meantime, while "Thetis" was in Windau, she underwent temporary repairs that allowed her to steam for Neufahrwassar on 21 August, proceeding then to Kiel, where she was decommissioned on 3 September in the "Kaiserliche Werft" for repairs.