Action of 9 February 1945

On 6 February 1945, U-864 passed through the Fedje area without being detected, but on 9 February Venturer heard U-864's engine noise. Launders had decided not to use ASDIC since it would betray his position and spotted the U-boat's periscope as her captain looked for his escort. In an unusually long engagement for a submarine, and in a situation for which neither crew had been trained, Launders waited 45 minutes after first contact before going to action stations. Launders was waiting for U-864 to surface and thus present an easier target. Upon realising they were being followed by the British submarine and that their escort had still not arrived, U-864 zig-zagged underwater in attempted evasive manoeuvres, with each submarine occasionally risking raising her periscope.

Venturer had only eight torpedoes as opposed to the 22 carried by U-864. After three hours Launders decided to make a prediction of U-864's zig-zag and released a spread of his torpedoes into its predicted course. This manual computation of a firing solution against a three-dimensionally manoeuvring target was the first occasion on which techniques were used and became the basis of modern computer-based torpedo targeting systems. Prior to this attack, no target had been sunk by torpedo where the firing ship had to consider the target's position in three-dimensional terms, where the depth of the target was variable and not a fixed value. The computation thus differs fundamentally from those performed by analogue torpedo fire-control computers which regarded the target in strictly 2D terms with a constant depth determined by the target's draught.

The torpedoes were released in 17-second intervals beginning at 12:12, and all taking four minutes to reach their target. Launders then dived Venturer suddenly to evade any retaliation. U-864 heard the torpedoes coming, dived deeper, and turned away to avoid them. The first three torpedoes were avoided, but U-864 unknowingly steered into the path of the fourth. Exploding, U-864 split in two, and sank with all hands coming to rest more than 150 metres (490 ft) below the surface. Launders was awarded a bar to his DSO for this action.

Merchant ships sunk

During her career, she sank five merchant ships all off the Norwegian coast.

Date	Name	Nationality	Tonnage[Note 1]	Location[4][5]
2 Mar 1944	Thor	Germany	5559	Stadlandet
15 Apr 1944	Friedrichshafen	Germany	1923	Egersund
11 Sep 1944	Vang	Norway	678	Lister
22 Jan 1945	Stockholm	Germany	618	Stavanger
19 Mar 1945	Sirius	Germany	1,350	Namsos