The sea was moderate, but visibility was no more than three-quarters of a mile. P. 61 kept on the convoy’s starboard bow and only about two cables ahead, zigzagging at seventeen knots. At three minutes to six in the morning, the oiler was suddenly observed to be settling by the stern. Lieut.-Commander Frank Arthur Worsley, R.N.R., on the bridge of P. 61, had heard no sound of explosion, and no one in the ship had sighted a submarine. The Commander knew, however, that in the thick mist and with a head wind and wash against him, this was natural enough. He immediately circled twice round the convoy, signalling to her: ‘Have you been torpedoed?’ With some difficulty she replied ‘Yes,’ and also that she had sighted the submarine. Lieut.-Commander Worsley ascertained that the _San Zeferino_ had her boats swung out and was in no immediate danger. He then reduced speed, in order not to betray his presence to the enemy, and started off north-west on the chase. Inevitably he soon lost sight of the oiler in the fog, and was obliged to turn in order to regain touch. He found the convoy still heading on her course, though her engines were wrecked; crossed her bows, and passed down her port side and under her stern. Directly P. 61 was clear, Lieutenant J. R. Stenhouse, R.N.R., on her bridge, sighted the enemy about half a mile away on the starboard beam, heading westward at nine knots. Action stations had already been sounded, and fire was now opened from the port 12-pounder gun. One round of common shell was sent into the submarine, striking her just before the conning-tower. But a gun action was not the final object of P. 61. Lieut.-Commander Worsley had got his engines up to full speed as he came on, and saw that the enemy could not escape his ram. So sure was he that, after three minutes’ run, he deliberately stopped both engines, so as to let the ship’s bows drop deeper in the water and make a better hit.