On 1 April 1941 (after the war had been raging for about a year and a half and the Battle of the Atlantic was well underway), Launders was posted to his first submarine assignment aboard HMS Umbra.

[1] Venturer was Launders' first submarine posting, but his intellect, quick thinking, and leadership had put him in position for just such a challenging command.

Venturer was a fast-attack "hunter-killer" sub, whose mission was to hunt for enemy shipping and other submarines, attack them, and to effect a speedy getaway without engaging in a prolonged action.

[2] a "boy-wonder with a genius for mathematics,"[2] which gave him a tremendous edge in making the necessary vector calculations (manual or minimally mechanical-computer assisted reckoning of speed and trajectories for targets, torpedoes, attacking vessels and currents) that were part of submarine warfare tactics of the day.

[2] Former Able Seaman and retired Royal Navy instructor Henry James Plummer also served aboard Venturer during the war with both Launders and Watson.

"[4] Venturer had sunk some thirteen German vessels during ten patrols over the previous twelve months,[2] including the Type VIIC U-boat U-771 off Norway's Lofoten Islands on 11 November 1944,[5] some 7 nautical miles (13 km) east of Andenes, Norway, resulting in Launders' appointment as a Companion of the Distinguished Service Order (DSO) "for courage, skill and undaunted devotion to duty".

U-864's top-secret manifest included jet-engine parts from the German Me 262 jet fighter plane that the Japanese were going to try to clone, missile guidance systems from Peenemünde, of the type used on the V-2 rocket, and many tonnes of mercury, a raw material that was in short supply in Japan that was vital to the industrial production of ordnance since it was a necessary component in the fabrication of detonators.

[2] U-864 had put into the U-boat pens in Bergen to repair damage from having run aground during their first attempt to set off on the mission (they had to take very round-about routes that were often not well charted to avoid Allied anti-submarine warfare patrols in the main shipping channels).

[2] However, their normally quiet engine started to make an abnormally loud, rhythmic noise that could be easily detected by any anti-submarine warfare equipment in the area.

Neither he nor anyone in the Nazi high command knew that the Enigma code, Germany's top-secret naval encryption system, had been broken by British mathematician Alan Turing and his cryptanalytics team at Bletchley Park.

[2] Wishing to deny the Japanese any advantage that might extend the war in the Pacific, Royal Navy Submarine Command dispatched Venturer to intercept and destroy U-864.

Launders received a brief message from Royal Navy Submarine Command as to the estimated whereabouts of U-864 (with reasonable precision, somewhere near the island of Fedje, off Norway's southwest coast, just north of the pens at Bergen), along with instructions to destroy her.

[2] Alternatively, as the German submarine was submerged with one or both diesel engines running, the object sighted by the officer of the watch may well have been its snorkel.

For their actions, several crewmen aboard Venturer were decorated by the Royal Navy, and Launders himself was awarded a bar to his DSO "for gallantry, judgment and skill in a successful patrol.