Coastal Command Tactical Instruction 41

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Staff Sergeant
Jul 2, 2006
Kiwi Land
Coastal Command Anti-Submarine Tactical Instruction
C.C.T.I. No. 41


This Anti-Submarine Tactical Instruction is issued with the primary object of
enabling aircraft to destroy U/Boats. All other results from attacks, such as
killing members of the crew, superficial damage by machine-gun fire or forcing
the U/Boat to dive, are of secondary importance.

2. A number of separate instructions on Anti-Submarine Tactics has been issued
by this Headquarters from time to time and numerous amendments added. These
instructions have been revised and consolidated into one, which cancels all
Coastal Command Tactical Instructions previously issued on this subject i.e.
Nos. 31, 33, 35, 36 and 40. In future, variations in tactical procedure will
be issued as amendments or addenda. Amplification of the instructions
contained herein will be found in Coastal Command Tactical Memoranda.

3. To kill U/Boats, crews must have a sound theoretical knowledge of:-

(i) The best means of sighting U/Boats.

(ii) The correct method of attack,

(iii) The correct procedure after attack.

4. The successful application of this theoretical knowledge is dependent on
continual practice. But neither theoretical perfection or practical
proficiency will be of any avail if, when the critical moment comes in a real
attack, the release mechanism for some reason or other fails to function
correctly. All Junior Commanders and Captains of aircraft should, therefore,
continually bear in mind:-

(i) The vital importance of air crews being given continual training in
delivering attacks.

(ii) The absolute necessity for eliminating any possibility of failures due
either to defective maintenance or faulty crew drill.


5. Good visual lookout by day and night is of outstanding importance in all
A/S operations. In order to bring their crews to maximum efficiency, captains
of aircrafts must carefully organise a watch system and train individual
members in both how and where to look.

6. There must always be at least two A/S lookouts who must keep a constant
watch while on duty. They should cover a 180° sector, i.e. from ahead to
90° on either side of the aircraft and one of them must invariably be
provided with Binoculars. Lookouts should be changed every half hour whenever
this is possible.

7. The area of sea to be searched must be at a sufficient range from the
aircraft - dependent on height and visibility - to give the crew a good chance
of sighting the U/Boat before the aircraft is itself observed.

8. Full details of how an efficient lookout can best be organised and
maintained are given in Coastal Command Tactical Memorandum No.50.


9. In addition to a visual lookout, it is essential that, subject to the
restrictions detailed in para. 10 below, that an efficient A.S.V. watch should
always be kept. The proper use of A.S.V. by day can be expected to increase
appreciably the total number of U/boats sighted and by night is indispensable.


10. There is no restriction on the use of A.S.V. Mk II by night, but except
when specially ordered it is not to be used by day on A/S patrols unless:-

(i) Visibility is under three miles.

(ii) Aircraft is flying above cloud in sufficient quantity to make
sighting of U/Boat unlikely at over three miles. A.S.V. should be
switched off at least 10 minutes before descending through cloud.

(iii) Required for navigational purposes.

11. When a Mk.II A.S.V. Blip fades and the operator is reasonably sure that it
was caused by a U/Boat, the following procedure should be adopted, except (a)
at night and (b) on convoy escorts:-

(i) Switch off A.S.V.

(ii) Leave area to a distance of at least 20 miles.

(iii) 20 to 30 minutes after leaving area, return without using A.S.V. at
height which will ensure maximum degree of surprise.

(iv) Should no sighting follow, continue duty ordered.


12. There are no restrictions upon the use of A.S.V. Mks. III, IV, V and VI,
and continuous watch by a trained WOP/AG must be maintained by day and night.
In order to ensure maximum efficiency, the Captain of aircraft should
carefully organise a tube watch system to enable operators to be changed at
suitable intervals, and so avoid eye fatigue which results in inefficiency.
Watch of the indicator should, when possible, not last more than 45 minutes,
when a relief watch must take over. The operator relinquishing watch should
then have a period of at least one hour on some other duty before returning to A.S.V. watch again.

13. The best height at which to fly on an A/S patrol is that which gives the
greatest chance of the aircraft surprising the U/Boat. In conditions of
moderate or good visibility, A/S patrols should therefore, be flown as
indicated below:-

(i) When there is no cloud or cloud is above 5,000 feet

Patrol height should be 5,000 feet. Pilots may, however, fly higher
if they wish, when confident that they can lose height sufficiently
quickly to make an effective attack.

(ii) When clouds are not more than 5/10th below 5,000 feet

Patrol above cloud, but not above 5,000 feet. Aircraft flying above
cloud should not normally fly directly over the cloud tops, but
preferably 500 to 1,000 feet above them.

(iii) When clouds are more than 5/10ths below 5,000 feet

Cloud cover to be used to the maximum to give concealment. Aircraft
should normally fly as near the cloud base as possible.

14. In conditions of low lying haze with good visibility above, U/Boats will
have only a limited horizontal view, while their view, upwards, will be little
affected. Aircraft should, under these conditions, fly much lower and at a
height calculated to reduce to the minimum the chances of being sighted, on
the assumption that an aircraft flying high will be seen by a U/Boat sooner
than one flying lower.


15. The normal A/S weapons at present in use are the 250 lb. Torpex-filled
depth charge and the 600 lb. Anti-Submarine Bomb.

Height Limitations

16. The height limitations of these two weapons are as follows:-

Maximum Height Minimum Height

250 lb. Depth Charge 500 feet. No limitation.

600 lb. A/S Bomb 5,000 feet. 500 feet.

Depth Settings

17. Pistols, in both the 250 lb. depth charge and the 600 lb. A/S Bomb should
be set at the shallowest settings. These are as follows:-

250 lb. D.C. 25 feet.

600 lb. A/S Bomb 35 feet (Set during manufacture).

Stick Spacings

18. When dropping a stick of 250 lb. Depth Charges by eye, the stick spacing
to be used is 100 feet, which has been proved over a period to give the best
all-round results.

19. When using the Mk.II(0)A and Mk.III Low Level Bomsight, stick spacings for
the 250 lb. D.C. are to be as follows (as soon as the necessary computor
charts have been issued):-

For sticks of six D.C.'s 60 feet
For sticks of four D.C.'s 100 feet
For sticks of two D.C.'s 100 feet (Distributor to be adjusted so that
these are dropped as Nos. 2 and 3 of an
imaginary stick of four).

20. The 600 lb. A/S Bomb should be employed in conjunction with the Mk.XIV
Bombsight, or the Mk.II(0)A or Mk.III Low Level Bombsights. It has not yet
been cleared for stick spacings less than 80 feet and will normally be dropped
in sticks of three, spaced 150 feet.


21. In a low level attack, height must be lost and the approach made in the
quickest possible manner. In doing so, however, the pilot must appreciate:-

(i) Whether, if flying direct to the target, he has time to get the
bomb-doors open (when applicable) and to get in all respects ready
for the attack.

(ii) Whether a direct diving approach will increase the speed of the
aircraft to a point which necessitates an adjustment to the bomb
distributor setting.

(iii) Although the attack may be carried out from any direction, it should
be delivered as near along track of the U/Boat as is possible in the

22. On the run-up, the pilot should aim to be not higher than 300 to 500 feet, when three-quarters of a mile to a mile from the target.

23. Pilots should keep a sharp lookout during the approach for alterations in
course by the U/Boat, whether it is diving or remaining on the surface.


24. In view of the recent introduction of new weapons and new sighting
devices, no standard method of attack can at present be laid down except for the low level attack, where depth charges are released by eye and in which
considerable experience has now been gained.

25. The aim of the attack must be to make the centre of the depth charge stick explode within lethal range of the centre of the U/Boat. To do this, factors to be considered are, the estimated forward speed of the submarine, the time of flight of the D.C.'s and their forward travel of 40 feet after entering the

26. In order to reduce errors to a minimum, depth charge attacks should be
delivered from low altitude. The normal height of release is 50 feet, and if
possible all Depth Charge attacks, when no sight is used, should be made from this height.

NOTE: The lethal range of the 250 lb. Depth Charge is 19 feet, and that of
the 600 lb. A/S bomb 28 feet.


27. In order to be able to make the necessary calculations quickly, regarding
the point of aim, the pilot or bomb aimer, as the case may be, must be fully
conversant with the following data:-

(i) The time from the release of a depth charge from 50 feet to
detonation at the shallow setting (25 feet) is approximately 5
seconds (2 seconds in the air and 3 in the water).

(ii) If the U/Boat is in process of crash-diving, her speed will be
approximately 6 knots (10 feet per second). Therefore, if the
U/Boat is attacked while some part of the hull is visible, the
centre of the stick should be aimed 5 x 10 = 50 feet ahead of the
conning tower (or its estimated position) at the time of release.
(If the conning tower is itself in sight, however, at the time of
release, it is desirable to make this the aiming point, although
theoretically, the stick will then fall 50 feet behind it.)

(iii) If the U/Boat has dived before the depth charges are released, (see
para. 32), the stick must be aimed a certain distance ahead of the
swirl, the apex of which is made by the foremost end of the conning
tower. This distance is, of course, that run by the submarine
between its final disappearance and the time of detonation of the
depth charges. Assuming that the speed of the U/Boat is 6 knots,
the distances are as follows:-

Time of Submersion to release of D.C.'s 5 secs. 10 secs. 15 secs. 20 secs. 25 secs. 30 secs.

Distance to aim ahead of swirl - 100 ft. 150 ft. 200 ft. 250 ft. 300 ft. 350 ft.

(iv) If the periscope only, is sighted, the speed of the U/Boat will
probably be only about 2 knots, i.e. 3.4 feet per second, hence the
stick should be aimed 5 x 3.4 = 17 feet ahead of the periscope at
the time of release.

NOTE: An additional allowance must always be made for the
under-water travel of the depth charges (40 feet).

28. The approximate length of a U/Boat's diving swirl is 100 feet and this can
be convieniently used as a yardstick in estimating the distance ahead that the
depth charges should enter the water.

29. The time lapse between submersion of the U/Boat and release of depth
charges must be known exactly. It should preferably be recorded by stop-watch and counted over the intercom. by a member of the crew previously detailed for this duty.

30. If the aircraft cannot deliver its attack until after the U/Boat has been
submerged for some time, the question always arises as to whether to attack or whether the D.C.'s should be saved for a probable second and better
opportunity later.

31. The pilot must in these circumstances, always use his own judgment whether to deliver an attack or not; but it is most unlikely that an attack with 250 lb. D.C.'s will be successful if the U/Boat has been submerged for more than 30 seconds at the time of detonation, unless it happens to have been seriously damaged previously.

32. A depth charge attack should not, therefore, usually be made after this
time limit, unless there is conclusive evidence of slow submersion or the
U/Boat is in the pilot's opinion, threatening a convoy or other surface craft,
or unless the attacking aircraft is nearing the end of its sortie. In these
circumstances, an attack may be made with a view to giving the U/Boat at least a bad shaking up, and in the case of a threat to shipping, preventing it
delivering its attack.

33. Owing to the increased lethal range of the 600 lb. A/S bomb and its
slightly deeper depth setting, this weapon has a good chance of being
effective if detonation occurs within 40 seconds of the U/Boat submerging.
When using this bomb, however, alowance must of course, always be made for the increase in time of fall. The time between release from 1,500 feet, for
example, and detonation at 35 feet would be approximately 10 seconds. As a
temporary measure, until sufficient data on which to assess the value of the
600 lb. A/S Bomb, is available, release may be made up to 40 seconds after
U/Boat has submerged.

34. If a U/Boat is sighted and no attack has been made, "baiting tactics" are
to be employed except when the aircraft is proceeding to escort a convoy, in
which case it should continue on its way. For details of "baiting tactics",
see paragraph 48 below.

35. Attacks are not to be made on oil streaks unless specifically ordered.


36. The number of depth charges to be released in any attack must always be left to the discretion of the Captain of the aircraft, according to the total
load carried and other circumstances at the time, but the following is given
as a general guide and should normally be adhered to:-

Aircraft on A/S Patrols or Sweeps -

37. (i) Aircraft carrying six or less depth charges should drop the whole
load in one stick.

(ii) Aircraft carrying more than six depth charges should drop sticks of
six leaving the remainder for subsequent use.

Aircraft on Escort Duty -

38. Aircraft on convoy or other escort duty should drop sticks of four depth
charges, leaving the remainder for subsequent attacks, e.g., an aircraft
carrying a total of six depth charges would drop four in the first attack
leaving two for a possible second attack, and an aircraft carrying twelve
depth charges will thus have sufficient for three attacks.

39. The Captain of the aircraft is, however, always at liberty to drop more
than four depth charges if he considers the chances of a second sighting
unlikely, e.g., when near his P.L.E. If he makes his first U/Boat sighting
when returning to base, he should always drop at least a full stick of six.

40. When a U/Boat is sighted by an aircraft which is en route to escort a
"threatened" convoy, an attack should be delivered only if a Class "A" Target
is presented, i.e., if the U/Boat is on the surface or has submerged for less
than 15 seconds, but not more than 50% of the depth charges, (and in any case a maximum of four) should be expended in these circumstances. When proceeding to a convoy not reported as "threatened", however, a full stick of four depth charges should always be dropped if the chances of a successful attack are considered good.


41. It is evident that U/Boat Commanders are now tending, increasingly, to
remain on the surface and fight back with their gun armament when attacked by aircraft. It is in fact, known that they have received orders to adopt these tactics if surprised on the surface, in such a way as to be unable to dive to a safe depth before the aircraft can deliver its attack.

42. When a U/Boat remains on the surface and fires at the attacking aircraft,
the decision as to the method of attack must rest with the Captain of the
aircraft who will take into consideration his armament, the degree of surprise
achieved, the presence or otherwise of A/S surface vessels and the extent to which he is committed to the attack when the U/Boat opens fire. In general, however, he must remember that the primary reason for his existence is, for the time being, to kill U/Boats and that a U/Boat on the surface presents a much better chance of a kill than one submerged. It is no coincidence that recently, by far the larger proportion of certain or probable kills have been U/Boats which stayed on the surface and fought back.

43. It should also be borne in mind that even a big aircraft properly handled
and using its guns well presents a difficult target for the gunners in the
necessarily cramped positions of a U/Boat, which in any sort of a sea is a
very poor gun platform and especially so if the sea is beam-on. While,
therefore, the tactics to be employed must be left to the Captain's judgment
the attack should, whenever possible, be pressed home at once, preferably from dead ahead, making full use of the front guns to kill the U/Boat's gun crews or at least to keep their heads down.

44. If, however, the Captain of aircraft considers the direct form of attack
undesirable, alternative tactics are to circle the U/Boat at such a range as
to bring accurate fire to bear, flying an irregular course with constant
variations in height and firing with as many guns as possible, until the
U/Boat's gunners are disabled or the U/Boat begins to dive; when the aircraft
must be prepared to make an immediate attack. While adopting these tactics, a very careful watch through binoculars shold always be maintained to ensure that the earliest possible warning is received of any intention on the part of the U/Boat to submerge.


45. After carrying out an attack on a U/Boat by day, the aircraft must drop a
marker beside the swirl. By nite the site of the attack is to be marked by
flame float, and whenever practicable, two flame floats should be dropped at
the same time as the depth charges.

46. The aircraft should then keep the area of attack under observation long
enough to observe results and if possible, determine the extent of the damage caused by the attack. Where there are indications, such as wreckage or persisting oil, or air bubbles, that the U/Boat may be forced to re-surface, the aircraft is to remain over the site and maintain position and height best suited for delivering another attack.

47. On other occasions, excepting, of course, when the U/Boat is definitely
sunk, and except when the aircraft is on convoy escort duty, or at night,
"baiting tactics" (see para. 48 below), are to be employed. Aircraft
proceeding en route to escort a convoy should not remain over the site of an
attack for a period longer than fifteen minutes.


48. In adopting "baiting tactics" the aircraft will set course from the
position of the attack to a distance of at least 30 miles and will remain
outside this range for not less than 30 minutes. The aircraft should then
return to the scene of the attack, taking full advantage of cloud, sun and
weather conditions for concealment, in the hope that the U/Boat will have
again surfaced.


49. Photographs are to be taken whenever possible and duties are to be
allotted as necessary to individual members of the crew prior to take-off.
The most important photographs are those recording the attack. The rear, or mirror camera is to be turned on at least five seconds before the release of the depth charges and must be kept on for a minimum of 15 seconds afterwards, throughout which period the pilot should make no alteration of course.

50. The Captain of aircraft must always appreciate the situation relative to
the task upon which he is engaged and bear in mind the order of precedence for the despatch of signals subsequent to the sighting and attack of a U/Boat.

51. Whenever a U/Boat is sighted by an aircraft on an A/S patrol or sweep, if
there is sufficient time and opportunity without interfering with the
efficiency of the attack, the Captain of aircraft will instruct the W/T
operator to transmit on his operational frequency the Group 465 from the Naval section of the Air Force code. The Group is to be preceded by his own
aircraft call-sign and will indicate that an attack is about to be made on a
U/Boat. If it is subsequently discovered that no U/Boat is present, a
cancellation must be sent immediately and an acknowledgement obtained from W/T control. This procedure does not apply to aircraft on a convoy escort, who are to make initial reports of sightings by R/T to the S.O. Escort (see para. 52 below). It may also be suspended in special circumstances, when the risk from enemy fighters is considered such as to justify wireless silence.

52. When engaged on escort duty, the Captain of Aircraft must, as soon as
possible inform the Senior Officer of the surface vessel of vessels of the
presence of any U/Boat sighted, giving the position as a bearing and distance
relative to the vessel(s) or in the case of convoys, relative to the centre of
the convoy. This report is to be made by R/T, or V/S, if R/T communication
cannot be established; co-ordinates for lattitude and longitude positions are
not to be used. The making of this report must not, however, be allowed to
prejudice the efficiency of the aircraft's attack on the U/Boat and will
usually be sent after the attack has been completed.

53. When an aircraft on convoy escort estimates that it has sunk a U/Boat, the report is to be made by V/S to S.O. Escort. Only if this is impossible is R/T to be used.

54. Aircraft on protective sweeps, when from a previous sighting the position
of the convoy is known and the aircraft is within 20 minutes' flying thereof,
will close the convoy and inform the S.O. Escort of the presence of a U/Boat
in the same way as in paragraph 52 above.

55. Signals reporting sightings and attacks of U/Boats are to be sent to base
as follows, unless special instructions have been issued to the contrary:-

(i) Immediately after the attack, when on A/S patrol or sweep.

(ii) Immediately after informing S.O. Escort when on escort duty, or on a
sweep where the aircraft is in sight of or in R/T communication with
S.O. Escort.

(iii) While closing on a convoy, when on a sweep, in the circumstances of
paragraph 54 above.

56. It is essential that the relevant information be passed to base in the
correct form and without delay. The signals to be sent on the completion of
an attack are as follows:-

(i) The Groups 465 and 472 together.

(ii) The Group 511, denoting also the type of attack, but not giving an
estimate of hits unless a direct bomb hit on the surface on a U/Boat
is actually seen.

(iii) If the U/Boat is forced to the surface after the attack in an
obviously damaged condition and remains there for an appreciable
time, the Group 512 should be sent. If this happens immediately
after the attack and before the Group 511 has been sent, the Group
512 may be sent in lieu.

(iv) If the U/Boat does not dive on being attacked, the Group 467 should
be sent.

(v) If, after either 512 or 467 has been sent, the U/Boat subsequently
dives, the Group 466 should be transmitted.

57. The first signal (Groups 465 and 472) should always be sent uncoded, i.e.
as it appears in the Naval section of the Air Force Code. All subsequent
signals and amplifying reports are to be sent in special "SYKO".

58. All future action either by S.O. Escorts or base depends on receiving
accurate reports from the aircraft. No signal is to be sent claiming the
destruction of a U/Boat unless there is complete and absolute certainty.
Probable destruction calls for an amplifying signal giving accurate details.
Amplifying reports on U/Boats disabled on the surface must be made at
intervals of not less than 15 minutes.

59. Pilots and W/T operators must be fully conversant with homing procedure
and must be prepared to home either surface vessels or other aircraft to the
scene of the attack with the minimum of delay.


60. For purposes of assessment and so that all possible lessons may be learned from every attack, it is essential that the most complete and detailed account should be available. This is only possible, whether the attack is by day or night, if the crew drill is such as to ensure that no detail has been
overlooked. Captains of aircraft must, therefore, allot tasks to respective
members of the crew so that each knows his duty in this respect whenever an attack is made.

61. Crews, on landing must be interrogated by the Intelligence Officer, so
that the Form Orange can be completed and at the same time, paras. 1 to 11 of C.C. Form Ubat should be compiled. The remainder of this form is to be
completed by the Squadron Commander or his deputy, in conjunction with the
Intelligence Officer, when the crew is rested; this should normally be done
within 24 hours. The story should be complete to the smallest detail and even facts which may appear irrelevant should be included. The best way to obtain such information is by informal discussion and when the whole incident has been thoroughly investigated a connected account should be written down and read by the crew. If they are satisfied, the Form Ubat can then be completed. It is appreciated that the Form, compiled in this way, may differ considerably from the Form Orange, but this is acceptable.

(Signed) J.C. SLESSOR
Air Marshal,
Air Officer Commanding-in-Chief,
Coastal Command.

12th June, 1943.
k9kiwi thank you for posting this ! wonder how much change if any for 1944 till wars end in coping with U-booten ?

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