There's a nice summary in the Royal Navy‘s official history, The Naval Staff Monograph, Volume 18, ages 293 and 294:

“U 61 proceeded north-east. She had only one torpedo left, but it scored a distinct success. This was against the Warner, a Queenstown “Q’ ship, Q 27 (Acting-Commander Thomas W. Biddlecombe, R.A.N.), which had been cruising off the Shannon since March 3, on her first trip. On March 13, at 8:45am, she was in 52°30'N, 11°W., steering S. 55E. at 10 knots when the wake of a torpedo was seen 100 yards off the port quarter. The helm was put hard a-starboard — too late — the torpedo struck her on the port quarter.

“She sank in 5 minutes. It was cold bleak day. The port lifeboat floated off. The starboard was lowered but was sucked in and capsized as the ship went down, injuring Lieutenant Milne very severely. The submarine then came up, and after picking up some of the men in the water, including the captain, navigating officer, and three ratings, went off with them as prisoners to the north-east. There was a heavy swell running. The water was very cold, and it took sometime for the port lifeboat to right the boat that had capsized. It was done at last, but meanwhile Lieutenant Milne had succumbed to his injuries and was buried at sea; some thirteen men were never seen again.

“By 6:40pm, the two boats had set sail for land which was sighted at dawn on March 14. At 1pm that afternoon the conning tower of a submarine rose from the sea. For a moment they thought they were to become prisoners. But it turned out to be D 3, which took them on board and landed them at Galway early on March 15.”