In January 1916 "Alcantara" embarked on the 10th Cruiser Squadron's G patrol. She was due to return to port on 1 March, but on the morning of 29 February 1916 she was north-east of Shetland "en route" to a rendezvous with "Andes" she intercepted the German merchant raider "Greif" disguised as the Norwegian merchant ship "Rena" out of Tønsberg, Norway. At 0915 hrs at a range of 6,000 yards "Alcantara" ordered "Greif" to stop for inspection, which she did. "Alcantara"s company went to Action Stations, she trained her guns on "Greif", closed to 2,000 yards and slowed to lower a cutter to put an armed guard aboard the suspect ship. At 0940 hrs "Greif" increased speed and opened fire. One source claims she raised the Imperial German war ensign (""Kriegsflagge""). However, "Alcantara"s captain, Thomas Wardle, reported that after lowering the Norwegian ensign "Greif" fought under no flag. The first shell hit "Alcantara"s bridge, disabling her steering gear, engine order telegraph and all telephones and killing or wounding a number of men. Captain Wardle ordered full speed and open fire at a range of 2,000 yards. A messenger was sent aft and got her after emergency steering gear connected. "Greif" turned to starboard and closed range to 750 yards. Several German shells hit "Alcantara" near her waterline, entering her stokehold bunkers and engine room. "Greif" tried to torpedo "Alcantara". Captain Wardle reported that evasive action at 1002 hrs allowed the torpedo to pass clear under "Alcantara"s stern, but another source states that a torpedo detonated amidships against "Alcantara"s port side. A shell from "Alcantara"s port after gun hit and detonated the ready ammunition for "Greif"s after gun, putting it out of action. By 1015 hrs "Greif" was badly afire by her bridge and seemed to have stopped. At 1022 hrs "Alcantara" saw boats leaving "Greif" and duly ceased fire. "Greif" then fired one more shot, and "Alcantara" duly returned fire. The one shot was later attributed to a shell left in the breech of an abandoned gun being fired by the heat of the fire now raging aboard "Greif".