 Complete the following phrase:  The ship continued to operate with the fleet through 1915, in addition to her U-boat flagship duties. While cruising off the mouth of the Weser river on 21 April, she accidentally collided with the torpedo boat , breaking her in half and sinking her. Hamburg had to be drydocked for repairs, though these were completed in time for the ship to participate in a fleet sortie on 1718 May. Another operation followed on 2930 May; the ship saw little activity until the fleet conducted another sweep into the North Sea on 1112 September, by which time the II. Führer der Torpedoboote 2nd Commander of Torpedo Boats, Kommodore Commodore Karl von Restorff had hoisted his flag aboard Hamburg. A final operation for 1915 took place on 2324 October. None of the years operations had resulted in contact with elements of the British Royal Navy. The fleet continued these operations in 1916, with sorties on 57 and 2526 March and 2122 and 2425 April, the last of which resulted in the 