[3] In 2013, Preisler and Sewell wrote that an air compressor may have been wrongly installed or had worn out causing the engine to misfire with "loud, fitful vibrations".

The British were reading the German cyphers of the Enigma machine and the Royal Navy was concerned the secret cargo might enable the Japanese to extend the duration of the Pacific War.

Probable that U-boats proceed to seaward off r/v[5]As Venturer continued her patrol of the waters around Fedje, at 9:32 a.m. the ASDIC operator noticed a faint Hydrophone Effect (HE) which faded, then came back forty minutes later, somewhat louder.

It was theoretically possible to compute a firing solution for time, distance, bearing and target depth but this had never been tried because it was assumed that performing the complex calculations would be impossible, plus there were unknown factors that had to be approximated.

Launders made the calculations and assumptions about U-864's defensive manoeuvres, then ordered the firing of all four of his bow torpedo tubes, diving immediately to avoid retaliation by U-864.

U-864 attempted to evade once it heard the torpedoes coming but lacked manoeuvrability in dives and turns; it took time to retract the snorkel, disengage the diesel and start the electric motors.