Chastise: Operation order

General

1. The inhabitants and industry of the Ruhr rely to a very large extent on the enormously costly water barrage dams in the Ruhr District. Destruction of TARGET X alone would bring about a serious shortage of water for drinking purposes and industrial supplies. This shortage might not be immediately apparent but would certainly take effect in the course of a few months. The additional destruction of one or more of the five major dams in the Ruhr area would greatly increase the effect and hasten the resulting shortage. TARGET Z is next in importance.

2. A substantial amount of damage would be done, and considerable local flooding would be caused immediately consequent on the breach of TARGET X. In fact it might well cause havoc in the Ruhr valley. There would be a large loss of electrical capacity in the Ruhr caused by destruction of hydro-electric plants, but also due to loss of cooling water for the large thermal plants.

3. In the Weser district the destruction of the TARGET Y would seriously hamper transport in the Mittelland Canal and in the Weser, and would probably lead to an almost complete cessation of the great volume of traffic now using these waterways.

4. The reservoirs usually reach their maximum capacity in May or June, after which the level slowly falls.

Enemy Defences

5. (a). TARGET X

There are three objects on the crest of this dam which may be a light AA gun. A light 30-gun AA position is situated below and to the North of the dam with a possible searchlight position nearby. A double line boom with timber spreaders is floating on the main reservoir at 100 to 300 feet from the dam. No other AA position or defence installation is known.

(b). TARGETS Y and Z

Information about the defences of these two dams will be given when PRU sorties have covered these areas.

(c). The last resort targets are unlikely to be defended.

INTENTION

6. To breach the following dams in order of priority as listed:-

i. TARGET D (GO938)
ii. TARGET E (GO935)
iii. TARGET F (GO933)

Execution

Code Name

7. This operation will be known by a code name which will be issued separately.

Date of Attack

8. The operation is to take place on the first suitable date after 15th May, 1943.

Effort

9. Twenty Special Lancasters from 617 Squadron.

Outline Plan

10. The twenty special Lancasters of 617 Squadron are to fly from base to target area and return in moonlight at low level by the routes given at Appendix A. The Squadron is to be divided into three main waves, viz:-

(a). 1st Wave. Is to consist of three sections, spaced at 10 minute intervals, each section consisting of three aircraft. They are to take the southern route to the target area and attack Target X. The attack is to be continued until the dam has been clearly breached. It is estimated that this might require three effective attacks. When this has been achieved the leader is to divert the remainder of this wave to Target Y, where similar tactics are to be followed. Should both X and Y be breached any remaining aircraft of this wave are to attack Target Z.

(b). 2nd Wave. Is to consist of five aircraft manned by the specially trained crews who are to take the Northern route to the target, but are to cross the enemy coast at the same time as the leading section of the 1st Wave. This 2nd Wave are to attack Target Z.

(c). 3rd Wave. Is to consist of the remaining 6 aircraft and is to form an airborne reserve under the control of Group HQ. They are to take the Southern route to the target but their time of take-off is to be such that they may be recalled before crossing before crossing the enemy coast if the 1st and 2nd Waves have breached all the targets.

Recall will probably not be possible unless the first section of the 1st Wave are at position 51°51’N, 03°00’E by Civil Twilight (Evening) + 30 minutes and the 3rd Wave must be at this position 2 hours 30 minutes later. Orders will be passed to aircraft on the Special Group Frequency if possible before they reach the enemy coast instructing them which target they are to attack. Failing receipt of this message aircraft are to proceed to X, Y and finally last resort targets in that order, attacking any which are not breached. Officer Commanding RAF Station, Scampton, is to arrange for individual aircraft to be detailed to specific last resort targets.

Detailed Plan

11. The 1st Wave is to take off in three sections each of three aircraft and fly to the target at low level by the route given in Appendix A. Sections are to be spaced at intervals of 10 minutes and are to fly in open formation. Height is not to exceed 1,500 feet over England. On leaving the English Coast aircraft are to descend to low level and set their altimeters to 60 feet using the spotlight altimeters for calibration. The QFF at various stages of the route is to be carefully noted. Aircraft are to remain at low level for the flight to the target and on the return journey at least until crossing a point at 03°00’ E.

12. An accurate landfall on the enemy coast is important but on no account should aircraft turn back if their landfall is not quite accurate. The routes selected should be free of all major opposition from flak but good map reading and crew co-operation is essential to keep aircraft on track. The enemy coast is to be crossed as low as possible both going in and coming out even if it is necessary to climb a little later for map reading.

13. On arriving at a point 10 miles from the target the leader of each section is to climb to about 1,000 feet. On seeing this all other aircraft are to listen out on VHF. Each aircraft is to call the leader of the wave on VHF on arriving at the target. Spinning of the special store is to be started 10 minutes before each aircraft attacks. The leader is to attack first and is then to control the attacks on TARGETS X and Y by all other aircraft of the 1st Wave using the signals procedure given at Appendix B.

14. Number 2 of the leading section of the 1st Wave is to act as deputy leader for the whole of the 1st Wave during the attack on TARGET X. Should the leader fall out No 2 of the leading section is to take over leadership, and No 3 deputy leadership, for the attack of TARGET X. For the attack of TARGET Y Number 4 is to take over deputy leadership, in which event No 7 id to be the deputy leader. All other aircraft are to return to base after completing their attack. The first three aircraft are to return by Route 1, the second three by Route 2 and the last three aircraft of this wave by Route 3.

15. The direction of attack of TARGET X is to be at right angles to the length of the target. The general direction of attack is, therefore, to be S.E to N.W. Aircraft are not to be diverted to TARGET Y until TARGET X has been breached. If TARGET X is breached, up to two additional aircraft may be used, at the discretion of the leader, to widen the breach in TARGET X providing at least three aircraft are diverted to attack TARGET Y.

16. Destruction of the Dam may take some time to become apparent and careful reconnaissance may be necessary to distinguish between breaching of the dam and the spilling over the top, which will follow each explosion.

17. When TARGET X is seen to be breached beyond all possible doubt the leader is to divert the remainder of the first Wave to TARGET Y by W/T and VHF where similar tactics are to be used for the attack of this target. The general direction of the attack of TARGET Y is to be from N.W to S.E. If TARGET Y is seen to be breached beyond all possible doubt all remaining aircraft of the 1st Wave are to be diverted by the leader to attack TARGET Z independently using the same tactics as the 2nd Wave.

18. For the attacks of both TARGETS X and Y the special range finder is to be used, the height of the attack is to be 60 feet and the ground speed 220 mph.

19. The 2nd Wave is to take off and fly to TARGET Z at low level by the Northern Route given in Appendix A. Aircraft are to cross the enemy coast in close concentration, but not in formation, at the same time, although at a different point, as the leading section of the 1st Wave. Aircraft of this wave will be controlled on the alternative VHF channel. The special stores are not to be spun for the attack of TARGET Z. Aircraft are to attack this target from N.W. to S.E. parallel to the length of the dam and are to aim to hit the water just short of the centre point of the dam about 15 to 20 feet out from the edge of the water. Attacks are to be made from the lowest practicable height at a speed of 180 mph IAS. Aircraft are to return to base independently. First two aircraft by Route 1; second two aircraft by Route 2 and the last by Route 3.

20. The 3rd Wave is to consist of the remaining aircraft and is to form an airborne reserve under the control of Group Headquarters. They are to fly to TARGET X is close concentration, but not in formation, at low level by the Southern Route given in Appendix A. These aircraft are to be at position 51°52’N, 03°00’E 2 hours 30 minutes after the leading section of the 1st Wave have crossed this point on their outward route to the target. Orders for the 3rd Wave will be passed to all aircraft on the special Group frequency, if possible before they reach the enemy coast, instructing them on which target they are to attack. Failing receipt of this message aircraft are to proceed to X, Y and, finally, last resort targets in that order, attacking any which are not breached. The 3rd Wave are to use tactics of attack similar to those used by the 1st Wave when attacking Targets X and Y except that attacks on last resort targets are to be made independently. After attacking, aircraft are to return to base independently at low level by any of the three return routes detailed in Appendix A. Aircraft attacking early should take Route 1; the next aircraft Route 2 and the last Route 3.

Method of Attack

21. Aircraft are to use the method of attack already practised. The pilot being responsible for line, the navigator for height, the air bomber for range and the flight engineer for speed.

22. The interval between the attacking aircraft is to be not less than three minutes on all targets.

23. On all targets except Target Z each aircraft is to fire a red verey cartridge immediately over the dam during the attack. Aircraft attacking Target Z are each to fire a red verey cartridge as they release their special store.

24. All aircraft are to fly left hand circuits in each target area keeping as low as possible when waiting their turn to attack.

Time of Attack

25. The time of attack of each wave is not important to within a few minutes. The time of crossing the enemy coast is, however, all important. ZERO HOUR, which will be given in the executive order, is, therefore, to be the time at which the first section of the 1st wave are to be at position 51°52’N, 03°00’E on the outward route to the target. This time will probably be Civil Twilight (EVENING) +30 minutes. At this time aircraft of the second wave should be about position 53°19’N, 04°00’E.

Routes

26. As in Appendix A.

Diversions

27. The whole essence of this operation is surprise, and to avoid bringing enemy defences to an unnecessary state of alertness, diversionary attacks will be carefully timed. HQBC will be asked to arrange the maximum possible diversionary attacks so that the first enemy RDF or other warning of the diversionary attacks occurs 20 minutes after the leading section of the 1st Wave crosses the enemy coast.

No diversionary attacks should be despatched which would cross the enemy coast for a period of one hour preceding the 3rd Wave. 15 minutes after the 3rd Wave cross the enemy coast further diversionary attacks should be made at maximum strength and should continue, if possible, until the 3rd Wave are clear of enemy territory on the return journey. Diversionary attacks below 2,000 ft should not be made in the area bounded by the points (51°00’N, 03°20’E), (51°20’N, 06°30’E), (51°00’N, 10°00’E), (52°00’N, 09°00’E), (53°20’N, 06°00’E).

HQBC will also be asked to arrange suitable weather reconnaissance to report in particular on the visibility in the target area at least in sufficient time to recall the Lancasters before they cross the enemy coast if the weather is unsuitable.

Armament

28.

Fuel

29. The Lancasters may take off at a maximum all up weight of 63,000lbs at +14 boost. As the modified store now weighs about 9,000lbs, 1750 gallons of petrol can be carried.

Navigation

30. HQBC are requested to arrange for the Eastern Chain, Stud 5 to be switched on at Z-20 minutes and to remain on for the whole of the operation. This should assist in making accurate landfall on the enemy coast at the correct time.

31. The route is to be carefully studied before flight and the outstanding features, obstructions and pinpoints noted, particularly water pinpoints. ETAs at each are to be carefully calculated and if any pinpoint is not found on ETA a search is to be made before proceeding to the next pinpoint. Aircraft may climb to 500 feet shortly before reaching each pinpoint if necessary to help map reading.

32. The maximum use is to be made of the Air Position Indicators.

Synchronisation of Watches

33. All watches are to be synchronised with BBC time before take off on the day of the operation.

Secrecy

34. Secrecy is VITAL. Knowledge of this operation is to be confined to the Station Commander, OC 617 Squadron and his two Flight Commanders until receipt of the EXECUTIVE signal. After crews are briefed they are to be impressed with the need for the utmost secrecy because of the possibility that the operation may be postponed should weather reconnaissance prove the weather to be unsuitable.

Reports

35. Each aircraft as soon as possible after it has attacked is to report by W/T on the normal Group operational frequency in accordance with Appendix B.

Special Devices

36. MANDREL and TINSEL are not to be fitted.

( MANDREL was an airborne radar noise jammer that countered the German FREYA radars by radiating signals to swamp the normal return echo, thereby obliterating formation size and range information. TINSEL and its predecessor GASTON provided airborne jamming of German defence R/T, disrupting voice communications between ground control stations and nightfighter crews.

TINSEL used a microphone mounted in an engine nacelle, linked to a radio transmitter. A German speaking crewman used the aircraft's normal radio receiver to search for fighter control R/T, then tuned TINSEL's transmitter to broadcast the engine noise on the same frequency.)

37. IFF is NOT to be used on the outward journey but normal procedure is to be followed on the homeward flight. Any aircraft returning early is NOT to use IFF except after Z+30 minutes for the 1st and 2nd Waves and after Z+3 hours for the 3rd Wave.

Nickels

38. Nickels are not to be dropped.

(Nickels was the code name for Psyops Leaflets often dropped along with the bomb load..ED)

INTERCOMMUNICATION

Wireless Silence

39. Strict W/T and W/T silence is to be maintained until after Z+30 minutes for the 1st and 2nd Waves and after Z+3 hours for the 3rd Wave. Any aircraft returning early is NOT to break W/T or R/T silence and is not to identify on MF/DF except after Z+30 minutes for the 1st and 2nd Waves after Z+3 hours for the 3rd Wave. Aircraft returning before that time are to cross the English Coast at 1,500 feet at the point of exit and proceed direct to base or the nearest suitable airfield. Otherwise, normal operational signals procedure is to be used except as modified by Appendix B.

MF/DF Section

40. Section D is to be used if required in accordance with Paragraph 39.

Executive Order

41. The executive order for the operation will be given by EXECUTIVE followed by the code word allotted, the date on which the operation is to take place and the time of Zero Hour in British Double Summer Time.

APPENDIX B TO 5 GROUP OPERATION ORDER NO. B.976

SIGNALS PROCEDURE

R/T

VHF R/T is to be the primary method of control. The frequency set up on Button A is to be employed. The frequency set up on Button C is to be used by the 2nd Wave and is also to serve as a reserve frequency. The codeword CODFISH sent by W/T is to bring this reserve frequency into force.

From take-off until zero hour all aircraft are to maintain a listening watch on the TR1196 R/T set using Button D. At 03°00’E the TR1196 R/T set is to be switched off. The VHF set is to be switched on 10 minutes before reaching the target and is to be used until one hour after the completion of the attack, when aircraft are to revert to the TR1196 R/T Button D (Darky).

All R/T is to be in simple language and is to conform to the system which has been practised on the ground.

In the event of the leader’s R/T failing he will inform either No 2 or No 4 by W/T and will hand over control, using the appropriate codeword.

In the event of the R/T receiver being u/s in any other aircraft, the aircraft is to call the leader by W/T and transmit the codeword “DEAFNESS” twice.

W/T

All aircraft are to maintain a continuous listening watch on 4090 KCs throughout the operation except when passing the “operations completed” signal on 3680 KCs. Half-hourly broadcasts will not be made by Group Headquarters on 4909 KCs and 3680 KCs whilst aircraft are over enemy territory. No other aircraft will be using 4090 KCs.

In the event of a complete failure of control on VHF (Buttons A and C) the leader of the first wave is to transmit by W/T the codeword “MERMAID” meaning “Jamming on all R/T, control by W/T for 1st Wave only”.

For the purpose of W/T control the following codeword are to be used:-

PRANGER - Attack Target X
NIGGER - Target X breached, divert to Target Y
DINGHY - Target Y breached, divert to Target Z
DANGER - Attack Target D
EDWARD - Attack Target E
FRASER - Attack Target F
MASON - All aircraft return to base
APPLE - First Wave listen out on Button A
CODFISH - Jamming on Button A, change to Button C
MERMAID - Jamming on all R/T, control by W/T
TULIP - No 2 take over control at Target X
CRACKING - No 4 take over control at Target Y
GILBERT - Attack last resort targets as detailed

The leader is to transmit appropriate codewords to Group Headquarters by W/T, using the “I” method. Group Headquarters will repeat the whole message twice, using full power.

Should W/T control be used, each aircraft is to call the leader of the Wave by W/T as soon as it arrives over the target. Instructions will then be given by the leader to attack the appropriate target.

All aircraft are to change to the normal Group operational frequency 3680 KCs as soon as the special weapon has been released and are to transmit the following code group and appropriate figure, or combination of figures, adding the letter of the Target Z, B, C, D or F after the figure or figures, e.g. GONER 78C :-

GONER 1 - Special weapon released. Failed to explode.
GONER 2 – Special weapon released. Overshot Dam.
GONER 3 – Special weapon released. Exploded more than 100 yards from Dam.
GONER 4 – Special weapon released. Exploded 100 yards from Dam.
GONER 5 – Special weapon released. Exploded 50 yards from Dam.
GONER 6 – Special weapon released. Exploded 5 yards from Dam.
GONER 7 – Special weapon released. Exploded in contact with Dam.
GONER 8 – No apparent breach.
GONER 9 – Small breach in Dam.
GONER 10 – Large breach in Dam.

When acknowledgement of the receipt of this signal has been received from Group Headquarters aircraft are to revert to the special Group Frequency 4090 KCs.

All aircraft W/T sets are to be accurately calibrated to 4090 KCs.

CALLSIGNS

R/T

W/T

Aircraft of First Wave - J9P
Aircraft of Second Wave - 5OM
Aircraft of Third Wave - JB5
617 Squadron collective - WB1
HQ 5 Group 4090 KCs control - 1MF
HQ 5 Group 3680 KCs control - B3S

VISUAL

Should R/T and W/T communications fail the leader and sub-leader of each Wave is to fire a constant series of green stars over or near the target area which will mean “Wait your turn to attack as best you can, when target is breached proceed to next target”.

APPENDIX A TO 5 GROUP OPERATION ORDER NO. B.976