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U-boat Tactics in
World War II
GORDON WILLIAMSON
ILLUSTRATED BY IAN PALMER
© Osprey Publishing • www.ospreypublishing.com
Elite • 183
U-boat Tactics
in
World War
II
GORDON WILLIAMSON
ILLUSTRATED BY IAN PALMER
Consultant editor
Martin Windrow
© Osprey Publishing • www.ospreypublishing.com
CONTENTS
INTRODUCTION
Basic chronology of the U-boat war in the Atlantic
4
CONVOY NIGHT SURFACE ATTACKS
The Kretschmer method, 1940–41
The official doctrine, 1943
5
DECK-GUN ATTACKS
The theory: rules for interception of merchant ships
The practice
The official doctrine
14
SOLO MISSIONS
U-47 at Scapa Flow The Mediterranean: U-81 and U-331
Far Eastern waters, 1943–44
North American waters, 1942
21
‘WOLF-PACK’ ATTACKS
‘Free hunting’
Patrol/reporting lines
Fast patrol lines
The turn of the tide
29
KRIEGSMARINE-LUFTWAFFE CO-OPERATION
The Fw 200C Condor
Combined air-sea strikes
37
ASSOCIATED EQUIPMENT
Bachstelze
(‘Wagtail’)
Midget submarines
40
OFFENSIVE WEAPONS
Torpedoes
Torpedo guidance systems
Mines
43
DEFENSIVE EQUIPMENT
Radar decoys
Sonar decoys
Protective coatings
49
DEFENSIVE TACTICS
Against warships
Against aircraft
55
SELECT BIBLIOGRAPHY
INDEX
63
64
© Osprey Publishing • www.ospreypublishing.com
U-BOAT TACTICS IN
WORLD WAR II
INTRODUCTION
From the small, early Type II coastal submarines, through to the handful of
advanced Type XXI and Type XXIII boats that got to sea in the final months,
German U-boat design and production was forced into continual development
and improvement to keep pace with wartime needs. Paramount among these
was the challenge of having to face increasingly effective Allied anti-submarine
warfare (ASW) efforts, and – like the submarines themselves – tactics for their
effective employment needed continuous analysis and adjustment.
Submarines were employed in a variety of roles, from coastal patrols,
through individual opportunist actions by single unsupported
U-boats – both in the Atlantic and in more distant
waters – to co-ordinated ‘wolf-pack’ ambushes far
out in the North Atlantic. Numerous tactics were
developed, some more successful than others, in
attempts to help submarine commanders achieve
combat success, and the Oberkommando der
Kriegsmarine (OKM – Navy High Command)
went as far as producing a
U-Boat Commander’s
Handbook
to disseminate the practical lessons
learned by the most successful captains.
We now know, of course – as they did not –
that from around August 1941 the U-Boat Arm
was hugely handicapped by the British cracking
of the Kriegsmarine’s ‘Enigma’-encrypted radio
traffic between boats at sea and the Befehlshaber
der Unterseeboote (Commander, Submarines – the
headquarters staff of Adm Karl Dönitz). The
Bletchley Park centre needed continual radio
intercepts and up-dated decryptions to supply the
consequent ‘Ultra’ intelligence, but this often
allowed the Allies to route convoys to frustrate
German interception, and even to deploy assets
to lie in wait at designated rendezvous between
far-ranging U-boats and their resupply ships.
Nevertheless, on the occasions when the Allies
© Osprey Publishing • www.ospreypublishing.com
Grossadmiral Karl Dönitz,
Commander Submarines and
later C-in-C Navy, whose own
younger son was lost in U-954
in May 1943. The care shown
by Dönitz for his crews’ welfare
and the interest he took in the
development of tactics
stemmed from his extensive
combat experience as a
U-boat officer in World War I.
(Deutsches U-Boot Museum)
4
failed to intercept or decrypt message
traffic, and the Germans applied the
requisite tactics effectively, the U-boats
were capable of inflicting devastating
damage on Allied shipping, particularly in
the vital North Atlantic sealanes upon
which the war effort in the European
theatre depended.
CONVOY NIGHT
SURFACE ATTACKS
Such attacks were pioneered by the most
successful of the ‘ace’ commanders,
Korvettenkapitän Otto Kretschmer, who
discovered early in the war that attacks on
convoys were easier when made on the
surface under the cover of darkness.
With the boat trimmed low in the water,
the small conning tower was very difficult
for any lookout on a merchantman or
warship to spot. A further benefit of
attacking on the surface was that the
U-boat, powered by its diesel engines,
could move much faster and further than it
could underwater when reliant on electrical
power. (For instance, the Type VII boat had
a top surface speed and range of
c.17
knots and 8,100 nautical miles, but the
submerged figures were 7.3 knots, and only 69 miles before recharging the
batteries.) Its surface speed would certainly be faster than that of the merchant
convoys, and of some of the smaller escorts protecting them. Additionally,
the escorts’ ‘Asdic’ (sonar) equipment – for acoustic underwater location and
ranging – could not detect a submarine running on the surface.
The U-boat would approach the convoy submerged, and, ideally, gain a
position on its beam and slightly ahead. Having identified a gap in the escort
screen, it would surface and ‘sprint’ through the perimeter screen and into the
heart of the convoy formation. An ideal attack position was at right angles
to the overlapping parallel columns of merchant ships, which would thus
present the widest possible target area. The real prizes for the U-boats were
the large oil tankers and munitions ships, which would be placed at the centre
of the convoy to give them the greatest protection. This precaution was to
some extent effective against attacks by submerged submarines – which
would struggle to penetrate deeply into the convoy without being detected by
the escorts’ Asdic – but not against surface attack.
At an ideal distance of somewhere between 400m and 1,000m, torpedoes
would be launched (the torpedo would not ‘arm’ until it had run about
300 metres). It was normal practice to launch a full salvo of torpedoes at
several targets rather than selecting a single ship for attack, for the simple
reason that once a torpedo had detonated and the convoy had become aware
of the U-boat’s presence further attacks became more difficult and dangerous.
© Osprey Publishing • www.ospreypublishing.com
Kapitänleutnant Kurt Diggins,
commanding the Type VIIC boat
U-458, is shown at the
navigation or ‘sky’ periscope in
the relatively spacious control
room. This larger of the two
periscopes was used
predominantly for scanning the
horizon and sky for enemy ships
and aircraft, and also to take
bearings. KL Diggins survived
the sinking of his boat in August
1943, and outlived the war.
(Deutsches U-Boot Museum)
5

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