[1] Rotors from Kriegsmarine's Enigma machine were captured from the survivors, the wiring of which was unknown at that time to British codebreakers at Bletchley Park.

The submarine was powered by two MAN M 6 V 40/46 four-stroke, six-cylinder diesel engines producing a total of 2,100 to 2,310 metric horsepower (1,540 to 1,700 kW; 2,070 to 2,280 shp) for use while surfaced, two BBC GG UB 720/8 double-acting electric motors producing a total of 750 metric horsepower (550 kW; 740 shp) for use while submerged.

[7] On Tuesday, 21 November 1939 at 08:30 in rough seas, the trawler FD87 Sulby (from Fleetwood), was sunk by gunfire from U-33 75–80 miles north-west of Rathlin Island.

[8] The crew had just managed to launch and push off the two lifeboats as the submarine fired two shells into the trawler amidships and she sank within two minutes.

The other lifeboat was lost with five men including the Skipper, Clarence Hudson; Mate John Michael (Jack) Dawson; and deck hands Raymond Randles, James Wood and R.A. Lister.

However, the minesweeper HMS Gleaner, captained by Lieutenant-Commander Hugh Price, detected the U-boat on the 12th and dropped depth charges over a period of several hours.

Before the boat was abandoned, the U-boat's secret Enigma rotors were distributed amongst a few of the crew, who were instructed to release them into the sea to avoid capture.