U46 was laid down on 25 February 1937 in Germaniawerft in Kiel, Germany. She commenced sea trials in September 1938, and went into service on 2 November 1938. A member of the 7th U-Boot Flotilla, and originally under the command of Kptl. Herbert Sohler, Oblt. Engelbert Endrass took over as U46’s second Commander in May 1940.
On 1 June 1940, U46 departed Kiel and headed for the North Atlantic. Within a very short time, Endrass was registering his first successes, when he sunk both the auxiliary cruiser Carinthia (20 277 grt.) and the finnish ship Margareta (2135 grt.) on the same day, 7 June 1940. Just 4 days later, Endrass sunk the Athelprince (8782 grt.), and a day later succeeded in sinking a further three ships, the Greek M. Hymettus (5820 grt.), and the two British ships Barbara Marie (4223 grt.) and Willowbank (5042 grt.). On 16 June Endrass then sank the Greek ship Elpis (4500 grt.) and 6 days later even made an unsuccessful attack on HMS Hood. On 1 July 1940, U46 arrived back in Kiel after what can be considered to be an extremely successful month.
On 1 August, U46 departed Kiel once again, making a four day stop at Bergen between 4 and 8 August, on her way to the North Atlantic. Endrass soon thereafter sank the Dutch ship Alcinous (6189 grt.) and made an attack on the Greek L. Valmas (2080 grt.), which although not sunk, was so badly damaged that she had to be towed to port and scrapped.
On 27 August, U46 was west of Ireland, and heading for an operations area off the north-west Irish coast. Her log book shows that it had been a relatively quiet day. Endrass states that he had not even received messages from other U-Boats. The day continued to be uneventful, only disturbed by two alarm dives when aeroplanes were spotted, and U46 continued her passage to Endrass’ intended destination, north-west of Ireland.That evening, however, just after 19:00 hours, Endrass discovered the British ship H.M.S. Dunvegan Castle.
A British twin screw steamer of 15 007 grt., with a length of 540 feet, Dunvegan Castle was built in Belfast by Harland & Wolff for the Union Castle Mail Steamship Co. Ltd., and launched on 26 March 1936. She was requisitioned in September 1939 and converted by Harland and Wolff to an armed merchant cruiser with her identical sister, Dunnottar Castle. In 1940, John Sidney Brew was serving on board and on 27 August, she was steaming off the western Irish coast as a part of a Freetown convoy, under the command of Captain H. Ardill, R.N.
At 19:08, the log book notes, "A steamer on the starboard. Steering a general course of 70-90°, large zig-zags...high speed (15-16 sea-miles)". Endrass decided to wait for sunset before getting closer. The log continues, "Enemy is a large passenger steamer, light gray, 16-20 000 tons, armed, probably merchant cruiser. Due to his extreme zig-zags, we can keep up well despite his high speed". As darkness fell, Dunvegan Castle decreased speed, but she was easily visible, the night sky making a clear shadow of her form. Endrass prepared to attack, but Dunvegan Castle became aware of U46’s presence and commenced a strong but short course of zig-zags.
At 21:47 Endrass fired a single torpedo, at a distance of 400 metres, which struck Dunvegan Castle at the quarterdeck. He notes in his log that nothing significant occurred and that Dunvegan Castle continued her passage slowly and in a large circle. He prepared U46 for a second attack but dived suddenly when he believed Dunvegan Castle was preparing to open fire on her. Ten minutes later, U46 resurfaced and found her still moving in a large circle but at an even slower speed. Endrass prepared for another attack.
The log continues, "22:12 second surface attack, single shot, hit engine-room. We wait a while to observe the results. Nothing special to see, suddenly come under artillery fire, alarm". Endrass dived U46 and kept her submerged for 30 minutes before resurfacing and observing, "Enemy lies there stopped, but seems to float well under the circumstances".
Then, "Steered closer again, 22:51 third attack, single shot, hit forward quarterdeck. Enemy begins to burn, sinks significantly deeper, heavy list. Now I think he’s had enough. Not even the best steamer can survive three hits, as well as a fire on board".
Endrass noted that during a period of some 2 hours several, sometimes large explosions were observed on board Dunvegan Castle. However, he had not yet identified her, noting further that "the form of the ship was very similar to that of the steamer Strathmore...[but]...it could not be definitely ascertained if it was her".
Dunvegan Castle had been severely damaged. Although she managed to stay afloat during the night, she sank early the next morning at 54° 50" N, 11° W. Considering that she had been torpedoed three times, she remained afloat for a long time, and her casualties were relatively light; four Officers and 23 Ratings were killed, and 12 were wounded, but 250 survived. H.M ships Primrose and Harvester picked up the survivors and landed them in Gourock, Scotland. John Sidney Brew was amongst them.
H.M.S. Primrose's Commanding Officer, an unnamed Lieutenant Commander, R.N.V.R., filed the following report on the incident to the Secretary of the Admiralty, dated 4 September 1940:"Report on Survivors of H.M.S. Dunvegan Castle"
"When in position 54° 58'N, 12° 03'W at 0140 on 28th. August, Primrose was ordered by C. in C. W.A.'s" [Commander in Chief Western Approaches] "2351/27 to attack" [a] "submarine in position 55°N, 11°W (reliable fix).
At 0300, having reached the indicated position, a light, subsequently identified as a burning ship, was observed as a loom only, bearing 075° and as Primrose"['s] "A/S gear was not working, course was altered for the light, full speed, to render assistance.
At 0500 the Dunvegan Castle was reached and found to be on fire fore and aft in position 55° 8'N, 9° 54'W. Communication was established with a patrolling aircraft which was requested to report the presence of submarines while Primrose was stopped picking up survivors.
A total of 160 ratings and 32 officers were picked up from a motor boat, three life boats (one waterlogged), two rafts and isolated swimmers, Primrose's seaboat being sent away.
0700 Harvester arrived, and at 0715 Primrose proceeded leaving the remainder of the survivors, believed to be one boat only, to Harvester. An issue of rum, food and clothing wwas [sic] supplied to survivors, who were all landed at Gourock Pier which was reached at 2300/28.
Reports in the press that aircraft directed rescue ships to the scene are incorrect so far as Primrose is concerned."
About a month afterwards, Captain Ardill wrote in a report to the Admiralty regarding the incident, "I cannot pay too high a tribute to the Captain, Officers and Ship's company of H.M.S. Primrose for their kindness and consideration shown to the survivors of H.M.S. Dunvegan Castle. Nothing was left undone that could be provided for the comfort of the latter. Having been up all night on the work of rescue, it was not until 2.0AM next night when the last rating left the ship at Gourock...."
In the same report, Ardill wrote, "Having been in command and responsible for the above ship, it is natural that one should ask oneself if there was anything we would have done differently or would wish to alter in similar circumstances. The attached are a few rough notes forwarded while still fresh in my memory." Amongst these were:
"Zig zagging on a dark night in a dangerous area. I am of the opinion that it is best to go through a dangerous area in darkness at maximum possible speed, this was 14 knots at the time in question, due to defects in the starboard engine. Having observed the track of [the] second torpedo to be most phosphorescent it is possible that a similar effect was produced by the bow wave and was visible to the submarine."
"The necessity of keeping boats turned in until required to be lowered. The whaler that was turned out on the star'd side was blown to pieces by the explosion of the first torpedo."
"I am satisfied that I remained on board as long as possible....I have since ascertained that the actual time of leaving was 0220. The ship was badly on fire, the depth charges and ready use ammunition was [sic] exploding at regular intervals liable to set alight to the floating oil fuel." This will of course explain Endrass' observance of several explosions over a period of some 2 hours. Ardill continues, "With a waterlogged boat it was just possible to get clear before the floating oil actually took fire."
U46’s log: "On the following day, the British Admiralty announced the sinking of the auxiliary cruiser Dunvegan Castle, 15007 tons, by a U-Boat". Commander Endrass continues, "I assume this is our sunk auxiliary cruiser". U46 retreated from the area at a compass direction of 200°, and continued her course towards the north-west Irish coast.