[Sailor Steve]

Umm...

the sixth torpedo at 05.25 hours broke the ship in two, the stern capsized and the bow sank slowly in position 53º43'N, 14º41'W.

From your link. It took six torpedoes, but Patroclus did indeed sink.

On the other hand an American sub had much the same experience. This is an account from USS Whale.

Fired three torpedoes. Three hits. One hit aft of his stack, the second blew wreckage up through forward hold and the third
hit aft. Target started turning toward us. Swung hard right and set up for a stern shot.

Fired single stern shot at range of 600 yards. Hit aft. This was a good hit, stopping the target cold. The target was
sinking by the stern, taking considerable port list. Took pictures, firmly convinced this was the graveyard of another
Japanese ship. Many of the crew had an opportunity to view the sinking ship through the periscope.

Having worked up to windward to observe target better, was astonished to find the fire under control and the list
corrected. Water was being pumped over the side through portable hoses. Fired another torpedo from the stern tube, but this
missed. Target was dead in the water, shooting wildly with deck guns.

Crew and passengers abandoned ship, although gun crew remained at posts. Target settled about ten feet overall and then
maintained its depth. Closed and fired sixth torpedo from bow tubes. This hit aft of superstructure depth.

Target still floating. Fired seventh torpedo from bow tubes. This hit with terrific concussion, but did not change trim or draft appreciably.
Fired eighth torpedo from stern tubes. This was heard to hit, but very little concussion was felt.

Getting dark. Target sinking slowly on an even keel, but still looks salvageable. There was no sign of life aboard,
although it was believed gun crews had not yet abandoned ship. Wishing to dispose of it before arrival of planes or rescue
ships, fired ninth torpedo. This hit right under stack and the explosion ripped away both sides of vessel about ten feet
below the main deck.

Target now settled more rapidly, the main deck being a few feet from wash condition at last observation. This vessel
had absorbed seven and possibly eight torpedo hits. The cargo must have been of such nature as to prevent her from sinking
more rapidly. Target was identified as the Heiyou Maru, 9,815 tons.

On retiring we found ourselves in the midst of eight boats full of survivors, approximately fifty men to each boat.
These men were dressed in both white and blue uniforms. One boat was passed close aboard, and survivors made ready to hit
the periscope with their oars.