THE U-BOAT WAR BEGINS 65
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Extent of British air
cover in May 1940
Allied merchant ships sunk
by U-boats to May 1940
U-boats sunk
to May 1940
FIRST BLOOD SEPTEMBER 1939–MAY 1940
Merchant vessels in the Atlantic gained protection
through the convoy system, which the British
had used successfully in World War I. Groups of
vessels were escorted by warships and provided
with air cover. Zigzagging in close formation, the
convoys presented difficult targets to the U-boats,
which favored lone quarry. By the end of 1939,
merchant losses were worrying for the Allies, but
not critical: 114 vessels had been sunk, but 5,500
boats had reached their destinations.
1
THE ATLANTIC FRONT WIDENS
MAY–JULY 1940
The German occupation of France and Norway
in the spring of 1940 provided new U-boat bases
on the Channel and Atlantic coasts, considerably
widening the submarines’ strike range. At the
same time, British resources were diverted to
the defense of the island, greatly reducing the
number of vessels available for escort duty and
planes for air cover. This led to a period of success
for the U-boats.
2
Extent of US air cover
US PATROLS IN THE WEST
MARCH–DECEMBER 1941
The US became increasingly involved in the war,
especially after the Lend-Lease Act in March 1941
(see pp.70–71). American B-24 Liberator and PBY
Catalina planes provided enhanced air cover in the
western Atlantic, while US factories built ships for
Allied use. From 1941, advances in shipborne
radar and other countermeasures helped Allied
vessels to avoid the U-boat threat. In addition,
the capture of a German Enigma machine (see
pp.170–171) helped the British to decipher
intelligence of the U-boats’ location.
4
Allied merchant ships sunk by U-boats,
Jun 1940–May 1941
U-boats sunk, Jun 1940–May 1941
ALLIED LOSSES SOAR
JUNE 1940–MAY 1941
In June 1940, the Germans employed a new tactic,
known as the wolf pack, to take on the convoy
system. Lines of U-boats patrolled the Atlantic,
and when one spotted a convoy, it would relay its
position and head back to base; a wolf pack of
U-boats would then gather, waiting for the cover
of nightfall to launch an assault. The results were
lethal: by March 1941 well over 3^1 ⁄ 4 million tons
(3 million metric tons) of shipping had been lost.
3
Oct 14, 1939 U-47
sinks the Royal Navy
battleship Royal Oak at
anchor in Scapa Flow.
Sep 3, 1939 Within
hours of the outbreak
of war, U-30 sinks the
British SS Athenia.
Jun 1941
The Soviet Union joins
the Allies after it is
invaded by Germany.
Sep 21–22, 1940
A German wolf pack
intercepts Convoy HX72,
sinking or damaging 14 ships.
Mar 16, 1941 Convoy
HX112’s escorts fight off
a wolf pack attack,
sinking two U-boats.
May 9, 1941 British
warships disable U-110,
seizing a codebook and
Enigma machine that will
help British code-breakers
at Bletchley Park decipher
German messages.
May 21, 1941 U-69 sinks the US
merchantman Robin Moor, showing that
the tropical Atlantic is no longer safe
even for US civilian vessels.
US_064-065_U-boat_War.indd 65 19/03/19 5:39 PM