Lessons Learned at Dieppe (I)

Fire Support, Headquarters, and Weather

In September of 1942, the Combined Operations Directorate published a précis of the lessons learned during the ill-fated landing at Dieppe. The text that follows, in this post and subsequent posts in the series, is a verbatim copy of the portion of that document called The Lessons in Detail.

343.  General Observation.  Many lessons were learnt at Dieppe, not all of them new.  The opportunity is taken of repeating and re-affirming the lessons learnt in previous operations as well.

344.  Naval Fire Support

The Lesson of Greatest Importance is the need for overwhelming fire support, including close support, during the initial stages of the attack.  It is not too much to say that, at present, no standard Naval vessel or craft has the necessary qualities to provide close inshore support.  Without such support, any assault on the enemy-occupied coast of Europe is more and more likely to fail as enemy defenses are extended and improved.  Further remarks on close support vessels will be found in paragraph 362 (a) below.

345.  The Formation of Assault Forces

(a)  For any amphibious campaign involving assaults on strongly defended coasts held by a determined enemy it is essential that the landing ships and craft required for the assaults shall be organized well in advance into Naval assault forces.  These must have a coherence and degree of permanence comparable to that of any first-line fighting formations.  The need for discipline, morale, tactical integration and flexibility and professional competence are not disputed in the case of troops, war vessels and air formations.  Precisely the same applies to assault ships and craft.

(b)  The great importance of adhering to sound Naval procedure and organization has been brought out not only at exercises, but also in operations.  While it is one of the objects of the Navy to land troops on the beach in the formation the Army desires, this must not be attempted at the expense of sacrificing principles of sound seamanship or of sound flotilla procedure especially where a night landing is concerned.  It is always the simplest form of organization which has the best chance of success.

(c)  It is also essential that the Army formations intended for amphibious assaults against opposition should be trained in close co-operation with the Naval assault forces that will carry them to the attack.

346.  The Need for a Combined Headquarters

(a)  The Naval, Military and Air Force Commanders and the Supreme Commander or officer responsible for launching the operation, will usually have their own headquarters many miles apart.  In Combined Operation Headquarters a permanent set of adjacent offices is provided specially for the Naval, Military, and Air Force Commanders and their staffs, for all operations mounted under the Chief of Combined Operations.

(b)  The vital difference made to the planning of a Combined Operation when the outline plan is prepared by an experienced Inter-Service staff and the detailed plan by Force Commanders and their staffs working and living together, has been amply demonstrated in the Vaagso, Bruneval and St. Nazaire raids, and was so again in the Dieppe operation.

(c)  During an assault it is, of course, essential that the Naval and Military Force commanders should be afloat in a specially equipped Headquarters ship, and thus able to get close enough to the battle to be in a position to take and implement decisions immediately effecting the course of action.

347.  Period During Which an Operation can be Undertaken

(a)  The overriding factor of all operations against the enemy on either side of the Channel is the weather.  Weather conditions need not be the same for all types of operations.  If a raid such as the assault on Dieppe is to be made, then the weather conditions under which it can be carried out differ from those which can be accepted in an operation involving a permanent landing on the enemy-occupied coast.  The problem is further complicated by the fact that conditions required by the Royal Navy are not necessarily suitable for the Royal Air Force and vice versa.

(b)  The Dieppe raid showed clearly that for a raid in which the Naval and land forces are given full air protection, good visibility is essential, and this overriding factor must be added to others equally indispensable.  The operation against Dieppe could not prudently have taken place if the cloud had been more than four- to five-tenths at 4,000 feet, if the wind had been more than Force 3, or if there had been an appreciable swell.  The sea had to be calm enough to make a withdrawal feasible.  These conditions seldom, if ever, occurred during June, July, and August, 1942.  

Furthermore, four previous operations had been postponed and subsequently cancelled because the weather conditions were worse than those required.  Even on 19th August, conditions were not ideal, and the force was sailed by the Chief of Combined Operations on a forecast which was by no means as favourable as could have been desired.  So much was this so that just before the actual departure, the Naval Force Commander received a message warning him that the weather might deteriorate, but he nevertheless took the risk of continuing, a decision which was fully justified by events.  It must also be borne in mind that the length of French coast within the advantageous fighter arena is also open to prevailing westerly winds, which were one of the main causes for the postponement of the four previous operations.  On the other hand, if Air co-operation can be dispensed with, then the number of days on which an operation can take place is increased, for calm days are often associated with fog and mist, conditions in which aircraft cannot operate with certainty, especially in the early morning.

(c)  The conditions governing an expedition in which the troops will remain on shore are different from those which must prevail during a raid.  If troops have not to be withdrawn they can be put ashore in much worse weather, with a wind of Force 5 or 6 and considerable swell.  Here, however, the limiting factors are their reinforcement and their maintenance.  To supply troops on shore over open beaches requires weather conditions similar to those needed for a raid, unless the abandonment on the beach, should the weather deteriorate, of the supply carrying craft in ever increasing numbers, can be expected.

(d)  The conclusion must, therefore, be that since it is unjustifiable to mount an oper-ation which cannot, with certainty, take place in the average year, it follows that a raid must be so planned as to be independent of tidal conditions in the greatest possible degree.  This was so in the Dieppe raid which could have been carried out in 12 days in any lunar month, thus making it virtually certain that it could take place during the summer for a succession of days in which the weather conditions are favourable on the landing beaches.  They are principally dependent on the time required to capture a port or sheltered waters of suitable dimensions. Such a succession of days can never be relied on when operating on beaches which all face one way and are lee shores in prevailing winds. Consequently an assault made with the intention of remaining ashore should be planned to take place in an area capable of being supplied over beaches which face in different directions, or in an area where a port or sheltered anchorage is likely to fall into our hands at a very early stage.  In other words, a plan based on the assumption that weather conditions will be uniform is very likely to fail and, therefore, a plan which can be carried out even when they are indifferent or bad is essential.