Churchill Archive for Schools - Themes_Key questions_Battle of the Atl

Was Churchill really worried about the Battle of the Atlantic? And if so, why?

Source 4

Notes from Frederick Lindemann to Churchill on aspects of anti-submarine warfare, dated 1941


 CHAR 20/258A/111-113

We've highlighted the parts of the document which appear in the transcription below.

Simplified Transcript

Various recent reports seem to show that we’re not making much progress in attacking submarines.

ASV (Air to surface vehicle, or attack by aircraft) is an advance in attacking submarines but the enemy often detects the aircraft and submerges. Even so, sending out ASV radio signals to fool U-boats might be a good way to protect ships.

Submarines use hydrophones or RDF to locate ships they attack. Our ships should be able to detect the U-boat’s hydrophone and turn into or away from the attack to make the ship a smaller target.

We’re investigating other devices but apparently asdic can give away the position of our ships as well as finding U-boats. We’re also working on magnetic detection of submarines from aircraft.

I trust that our ships are keeping radio silence so they can’t be detected although a German prisoner tells us they don’t always do this.

Original Transcript

6th January, 1941
Prime Minister.

Various papers submitted recently seem to show that progress with technical anti-submarine measures has not been very rapid.

ASV (Air to Surface Vehicle) marks a step in advance, but it seems to be believed that the enemy detects it (as he could easily do) and submerges before the aircraft can reach him. If this be so, sending out wireless signals of the A.S.V. type from ships when no aircraft is present might be worth considering so as to frighten the enemy off the surface.

If it is true that submarines brown convoys from a great distance in darkness they probably use either R.D.F or hydrophones to locate them. Since it should be feasible with our hydrophones to hear the salvo of torpedoes as soon as they enter the water, the well-known precaution of turning into or away from the enemy, has no doubt been considered. Since the torpedo must be quite a long time on the way, it might be possible, even, for merchantmen, to go hard a-port or a-starboard with advantage, unless the ships are very close together indeed.

It seems to be believed that the enemy does not use R.D.F. If he did it should be possible to locate him by his


own signals. Furthermore, decoy dipoles could be used …

Enemy submarines almost certainly use hydrophones with which ships can be heard at great distances. Indeed I have been told that we dare not use asdics for searching near convoys lest they give away our own position to an enemy equipped in this way. Here again the possibility of decoy noises seems to deserve study. Our investigations on the acoustic mine should be a help

For a long time now work has been proceeding on magnetic detection of submarines. This is probably feasible up to 200 feet. As this can be worked from a low-flying aeroplane it would seem worth pressing forward.


I trust rigid measures are taken to ensure wireless silence on the part of our ships. I hear unofficially that a German prisoner had stated that our vessels were frequently located by their failure to observe this elementary precaution.

What is this source?

This is a briefing note from Frederick Lindemann to Churchill about anti-submarine warfare measures. Lindemann was Churchill’s chief scientific adviser (and a friend; Churchill called him ‘the Prof’). In this report Lindemann is trying to summarise the various technologies which the Allies can use and which the British think the U-boats might be using.

Background to this source

In 1940 (the first full year of the war) 1059 Allied ships were sunk, 471 by submarine . As Britain now faced the Axis Powers alone, after the defeat of France in June 1940, Britain depended on imports to both feed its people and re-equip its armed forces, much of whose equipment had been left behind on the beaches of Dunkirk. It was imperative that effective measures were developed to meet the risk of U-boats.

It wasn’t a surprise that the Germans used U-boats to attack British shipping as this had happened in the First World War. In both that war and this one, the Royal Navy had to find new ways to defend British shipping and to attack the U-boats. The biggest challenge was actually locating U-boats in the first place. Once they were located they could be attacked effectively from ships or by aircraft.

How can we use this source in the investigation?

Remember, we’re hoping that this source can be useful to us in investigating why Winston Churchill was so worried about the Battle of the Atlantic. Sources usually help historians in two ways:

Surface level

  1. What is the state of progress on anti-submarine measures?
  2. What do the Germans use to detect Allied shipping?
  3. What do the Allies use to detect German submarines?
  4. What role can aircraft play?
  5. According to Lindemann, what part is science playing in the war against the U-boats?

Deeper level

Which of the inferences below can be made from this source?

On a scale of 1-5 how far do you agree that this source supports this inference? Which extract(s) from the source support your argument?
The Allies know how German submarines detect Allied shipping

The German prisoner hasn’t helped the Allies at all.

Lindemann is very optimistic about the Battle of the Atlantic.

Churchill would have been relieved, once he’d read this paper.

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Need help interpreting the source?

  • ASV means Air to Surface Vehicle – essentially an attack on a U-boat by an aircraft.
  • RDF means radio direction finding – listening to an enemy’s radio signals and trying to trace his location from them.
  • Hydrophones were devices which listened for sounds in the water. Skilled operators could tell ships, submarines and torpedoes from their sound.
  • Asdic was another system using sound to detect submarines underwater.

 Source 5

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