The report has the heading "Analysis of an Attack by a U-boat on Convoy OG 47 on 21st December 1940" - the culprit was the Italian submarine Mocenigo (Agostini), and the Swedish Mangen (cargo of 1396 tons coal) was sunk with the loss of 8 lives.

The references used to compile this report at the time were:
T.D. (C) .116/41 - Commodore's report
A/S.W.141/41 - Report of Proceedings and track chart of HMS Leith.
I.D. Form A.C. compiled by Commodore and Commanding Officer, HMS Leith.
30.12.40 - Report by Master S.S. Mangen.

Escort:
HMS Leith - 1,500 yards ahead of Convoy zig-zagging independently.

Particulars of Convoy
No. of Ships - 19 (Arnold Hague says the convoy had 30 ships - some ships may have been bound for North America and if so, would have detached early in the voyage)
No. of columns - 5
Course and Speed - 133° at 7 1/2 knots
Was Convoy zig-zagging? - No
Commodore's Ship - Egyptian Prince (31)

Weather
Wind - N.W. Force 4
Weather - Dark, clear, starry night
Visibility - 1 mile
Sea - Slight; moderate N.W. swell.

Events preceding the attack
From the Admiralty U-boat disposition signal of 18th December, (A.M.1322/18/12), it appeared possible that an Italian U-boat returning to Bordeaux from the Azores, would pass close to Convoy OG 47 on the 20th or 21st December. Because of this, the convoy used evasive steering throughout 21st December.

The Convoy, which had been steering 153°, altered course 20° to port at 2100/21, and at the time of the attack was steering a steady course of 133° at 7 1/2 knots. Leith, the sole escort, was stationed 1,500 yards ahead of the convoy and was carrying out an independent zig-zag.

At 2114 on 21st December, when in position 40° 47'N 16° 47'W, a lookout onboard Swedish S.S. Mangen (11), leading ship of the port wing column, reported a white line of foam in the water which passed underneath the ship from port to starboard.

Three minutes later, at 2117, Mangen (11) was struck by a torpedo on her port side under the bridge and the ship sank in three minutes.

At 2125 the Commodore signalled an emergency turn of 40° to starboard and increased to the full speed of the convoy, which was 10 knots.

S.S. Garm (14), rear ship of the port wing column, observing lights in the water, stopped to pick up survivors.

It is reliably reported that two more explosions were heard shortly after Mangen was torpedoed and it was surmised that these were torpedoes exploding at the end of their run.

Escort's Movements
On hearing the explosion, Leith, who had been on the starboard leg of the zig-zag for five minutes, increased to full speed and commenced an asdic and starshell search to port as shown in the track chart. At no time during this search was anything seen nor was any contact obtained.

Click in picture to enlarge.

At 2314 Leith returned to Garm who had been searching for additional survivors. As Garm's full speed was only 8 1/2 knots, she was ordered to proceed independently to Lisbon.

Leith then proceeded to rejoin the convoy which had resumed its previous course and speed at 2325.

Movements of the U-boat
It is believed that the U-boat which carried out this attack was Italian, and that she had been patrolling near the Azores.

Her movements and the tactics she employed while closing the convoy are unknown, beyond the fact that the attack was carried out from outside the port wing of the convoy. The positions and movements of the U-boat shown on the track chart only represent one possible course of action.

This U-boat is thought to have attacked S.S. Sarastone, a straggler from Convoy OG 47, in position 41° 18'N 15° 14'W at 1611 on the following day, and then to have returned to Bordeaux. The attack on Sarastone was repelled by the spirited action of the ship, in fighting her gun with such success that the U-boat broke off the action and retired, probably slightly damaged.

Related external links:
Italian Submarines in WW II - Mangen and Sarastone are mentioned on this page.

Chronological list of OG Convoys

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