After leaving port in March disguised as the Norwegian freighter Rena Norge, Leopard set sail on its mission to disrupt Allied commerce. On 17 March, the cruiser HMS Achilles stopped Leopard in the Atlantic, out-gunned, Laffert had no option but to proceed to the boarding vessel. Day dispatched a launch containing a boarding party of an officer, Laffert realised that he was about to be discovered, detained the party, and after about an hour fired two torpedoes at Dundee. Dundee manoeuvred out of the way just in time and the torpedoes missed by 20 yards, day ordered his gun crews to open fire and shells hit Leopard from the stern at such close range that every shot was a hit, smoke and steam rising from Leopard. Leopard turned to starboard but Dundee turned to port to avoid a broadside, by this time Leopard had been hit forty times. Achilles was 4 nautical miles to the east-north-east and opened fire on the raider about five minutes after Dundee had commenced firing, as Dundee avoided another broadside, Leopards gunners fired wild as she sailed straight for Achilles to avoid the fall of shot. Leopard continued to fire for about an hour more, while shells from Achilless heavy guns caused explosions and jets of flame. Leopard began to sink but the continued to fire, at 4,30 p. m. Leopard sank with all 319 hands. Damage to the British vessels was light and the casualties were the six members of the boarding party members on Leopard when it sank. Action of H. M. Ships Achilles and Dundee - Naval Despatch dated 21st March 1917
Right elevation and plan view from Brassey's Naval Annual of the Warrior class; the shaded areas show armour.