At 16.30 hours on 24 Dec 1944 the unescorted Robert J. Walker (Master Murdock D. MacRae) was hit by one torpedo from U-862 while steaming on a zigzag course at 10.8 knots about 165 miles southeast of Sydney, Australia. The torpedo struck on the starboard side in the stern, blew off the rudder, created a hole three by six feet, bent the shaft and destroyed the steering gear. When the unmaneuverable ship turned southward another torpedo was spotted at 18.20 hours about 1000 yards off the starboard side. One of the armed guards opened fire with a 20mm gun and exploded it about 100 yards from the ship. The crew then threw smoke floats overboard that screened the vessel for about 45 minutes.

At 20.00 hours, a third torpedo was spotted again about 1000 yards off the starboard side, but this time the gunfire was not effective and it struck at the #4 hold, creating a hole of ten by 20 feet on starboard and a hole six by eight feet on the port side. The blast ruptured the #3 deep tank and threw oil and water over the ship. After the second hit the survivors among the ten officers, 32 crewmen, 26 armed guards (the ship was armed with one 5in, one 3in and eight 20mm guns) and one passenger abandoned ship in three lifeboats and four rafts. Two crewmen were lost. The survivors were picked up after about 24 hours by the HMAS Quickmatch (G 92) and landed three days later at Sydney.
The Robert J. Walker sank about 17.00 hours on 25 December. U-862 had fired five torpedoes in the attack and became the only German U-boat that sank a ship in the Pacific Ocean.