John Cotesworth Slessor
University of Alabama Press
2009 (Original 1935)



Slessor was born in 1897. He joined the RFC in 1915 and flew on the Western Front between 1915 and 1918. During this period he was a appointed as a Flight Commander and spent four months as an Artillery and Infantry Coordination Officer. When the war ended, he was the Acting Commandant of the Central Flying School. Prior to writing Ari Power and Armies, Slessor completed flying tours at 1FTS and commanding a squadron in India; staff tours at the Directorate of Training, Directorate of Operations and Intelligence and as DS at the Army Staff College. Slessor was a graudate of both the RAF and Army Staff Colleges. He completed Air Power and Armies while OC of No. 3 (Indian ) Wing.

After 1935, Slessor would complete wartime service as AOC No.5 Group of Bomber Command, AOC Coastal Command and Deputy Air Commander in Chief - Mediterranean Air Forces. After the war he would serve as Air Member Personnel, Commandant of the Imperial Defence College and Chief of the Air Staff. He retired as a Marshal of the Royal Air Force.


Air Power and Armies is based on the lectures Slessor delivered while on staff at the Army Staff College. It draws heavily on his experience in the First World War and reflects an attempt to educate both Army and Air Force officers on the requirements for the effective employment of air power in support of a land campaign.

Slessor’s work is unique for the period as most other air power thinkers were advocating air power’s ability to conduct strategic operations, and provide a war winning capability. Slessor states clearly on p.3 his belief that the primary means of victory in future wars will be through “direct action [by air power] against the hostile vital centres.” However, in some situations, such as where it is necessary to seize and hold air bases closer to the enemy, land campaigns may be required. In these situations it is necessary for both land and air commanders to understand the how best to integrate their operations. Slessor wrote this book to identify the lessons from the First World War that can be used to help understand how to achieve this integration.


The book is divided into four parts:

  1. Air Superiority - Examines why air superiority is important, and ways it can be achieved.
  2. Selection of Objectives - Examines how the objectives for air power should be selected. This includes a discussion on when strategic operations should be conducted against industry while a land campaign is being conducted,
  3. Battle of Amiens - Examines the RAF experience at the Battle of Amiens to identify lessons and propose alternative solutions.
  4. Conclusion - Slessor ties up the book stating that air power has revolutionised war, and that it is difficult to predict exactly what the long terms results will be.


Air Power and Armies is based on the lessons of the First World War. Slessor research is extensive and comprehensive. He examines more than simply the operations on the Western Front, drawing lessons from Palestine, the Sinai, Mesopotamia and the Dardenelles. The Official History is the primary source used, and, where possible, Slessor provides direct quotes from orders to support his analysis.

Central ThemeEdit

Slessor argues that the key to effective air power is concentration at the decisive point in time and space. Determining what this is will be situation dependent and cannot be prescribed in advance.

  • The answer is, of course, that we must make full use of the mobility and tactical flexibility of air power; and concentrate the maximum force on whatever task is likely to be decisive, or to contribute most usefully to an ultimate decision, at the time. This is a principle of supreme importance in air warfare, and is in fact the key to the whole strategy of air power. (p.70)
  • And it should have been used concentrated, where its influence was most likely to be decisive at the time—whether in defence against the great German offensive, or in attack, as at Amiens on August 8th, or against the enemy sources of production on German soil. (p.79)
  • The whole art of air warfare is first the capacity to select the correct objective at the time, namely that on which attack is likely to be decisive, or to contribute most effectively to an ultimate decision; and then to concentrate against it the maximum possible force, leaving only the essential minimum elsewhere for security—and possibly to contain superior enemy detachments. (pp.82-83
  • But it [attacks on German war industry by the Independent Force] should have been done only at the proper time, and the proper time was not when the Allied armies in France were fighting with their backs to the wall for their very existence. (p.78)

Supporting PropositionsEdit

Other keys themes discussed by Slessor include:

  • The role of genius in air warfare
  • Gaining air superiority must be the first aim of the air force.
  • Requirements for centralised control to ensure effective air power
  • The aircraft is not a battlefield weapon
  • Aim of air power in support of land campaigns should be to isolate the battlefield.
  • Primacy of the offensive.

Role of geniusEdit

Slessor acknowledges that there is a certain degree of intelligence involved in the planning and execution of an air campaign. This is not a topic that was raised by previous air power theorists.

  • It must be sufficient to say that that experience, such as it is, does provide good grounds for the belief that sooner or later the side whose offensive is most intelligently directed, which is superior in the art of command, and whose morale, discipline, technique, and material efficiency is the higher—not only in the armed forces but in the nation as a whole—will surely, though possibly slowly, begin to impose its will upon the other. (pp.18-19)
  • The moral is, of course, that an air force commander must deliberately make use of this extraordinary capacity for effective diversion to attain air superiority at the really decisive point. He must exploit the extreme flexibility, the high tactical mobility, and the supreme offensive quality inherent in air forces, to mystify and mislead his enemy, and so to threaten his various vital centres as to compel him to be dangerously weak at the point which is really decisive at the time. (p.25)
  • To sum up, offensive patrols over enemy aerodromes are usually the best and surest way of bringing an enemy to action; but they must often be combined with other methods, and they must always be intelligently planned and co-ordinated with other forms of air activity. (p.45)

Importance of air superiorityEdit

Part I of Air Power and Armies is dedicated to the concept of air superiority, Slessor approaches the concept is a way that explains it with reference to the conduct of army co-operation and support missions. The thrust of the argument is that effective army co-operation is predicated on at least local air superiority,

  • But it is broadly true to say that up to the end of the war the primary object of all our operations, with one exception, was to secure air superiority over the battle line, to enable our reconnaissance and artillery aircraft to carry on their work of close co-operation. The one exception was the group of units known as the Independent Force R.A.F. (p.2)
  • Air superiority is only a means to an end and, unless it is kept in its proper place as such, is liable to lead to waste of effort and dispersion of force. (p.4)
  • Air superiority will be gained and will have to be constantly maintained by striking direct at those objectives which are of first importance to the enemy at the time, whatever they may be; and by persisting in this line of action against opposition and in spite of casualties, assisted in varying degree by diversions in the form of direct attack on the enemy’s air forces. (p.10)
  • The ideal method obviously would be to destroy the hostile aircraft, either in the air or on the ground. But since it will usually be impracticable to make certain of destroying the aircraft themselves to a sufficient extent, our efforts in that direction must be supplemented by action to dislocate and disorganize the aerodromes, workshops, and depots on which they must rely for maintenance equipment, and supply. The next most effective method to the actual destruction of an aeroplane is to stop it flying for lack of spare parts, fuel, or technical maintenance. (p.31)

Centralised controlEdit

Centralised control is critical to achieving the concentration of force required for the effective employment of air power. Slessor supports this through his analysis of the Battle of Amiens.

  • But concentration of air strength does not involve the assembly of vast masses of aircraft on one group of aerodromes in a circumscribed area … It means merely that the whole effort of all the squadrons involved is directed under unified control on a single co-ordinated plan, and its most essential requisite is a first-class signal organization. (p.189)
  • At the battle of Amiens the commanders concerned were the 5th Brigade (two bombers and eight fighters) under the orders of the Fourth Army Commander, the 9th Brigade, who received their orders direct from the A.O.C. at G.H.Q., and the 3rd Brigade (two bombers and four fighters), who were under the orders of the Third Army but who also (rather curiously) received orders from the A.O.G. at G.H.Q. … four different commanders were concerned in the direction of the air effort in this one battle— subject to a certain amount of co-ordination by British G.H.Q. … On the ground one British General was fighting the battle—General Rawlinson—and he and his staff should surely have had to deal with one single air commander and one only. (pp.195-196)
  • Only by some such means [centralised control] could the air situation on the entire front have been surveyed as a whole, and the combined efforts of all the Allied air striking forces have been properly co-ordinated and directed to the attainment of the one common object. (p.196)

Aircraft are not battlefield weapons

By this, Slessor meant that aircraft should not be regarded as merely long range, or more controlable artillery. Air power should be employed beyond the immediate battle area in order to optimise its utility to the land force.

  • The aeroplane is not a battle-field weapon—the air striking force is not as a rule best employed in the actual zone in which the armies are in contact. (p.90)
  • In theory a sound economy of force should require that a highly mobile weapon like an aeroplane should not be used to engage targets which can equally well be taken on by other less mobile weapons on the ground. (p.90)
  • On November 22nd, [1918 at the Battle of Cambrai] for instance, the majority of the assault aircraft were engaged—very gallantly and at a terrible cost in casualties—in close co-operation with the infantry, attacking enemy machine-guns and forward troops in the desperate fighting about Bourlon Hill and the village of Fontaine. Meanwhile, behind the battle-field, the medium reconnaissance aircraft were reporting 'a congestion of trains in Douai station—much movement south from that railhead— columns of troops and transport marching on Cambrai from Douai-other columns moving south on the Lens-Douai road' —and other similar movements, most of which were allowed to continue entirely unhindered from the air. (p.91)

Isolation of the battlefield

Proceeding on from the above, Slessor argues that the aim of the airplane in support of land operations is to isolate the battlefield from the enemy’s communications and supply lines.

  • So in this battle—as, indeed, in any battle on land—the object of he air force, or perhaps it would be more accurate to say the intention of the commander for the air force, should be to isolate the battlefield from enemy reinforcement and supply—it being, of course, understood that at the same time and largely by the same means our own lines of communication must be protected against enemy air action. (p.167)
  • This, then, should be the governing principle in the employment of the air striking force in a battle on land—isolation of the battle-field from enemy reinforcement and supply. (p.168)
  • The role of the air will be to create those difficulties [in the maintenance of a modern army] where they do not already exist, and to intensify when they do. (p.201)

Primacy of the Offensive

Slessor accords with the dominant British interwar preference for the offensive employment of air power.

  • The moral advantages of an offensive policy in any form of war will scarcely be questioned. (p.18)
  • Air forces can only be destroyed or neutralized effectively by the adoption of an active and persistent offensive in the air— whether the underlying strategical policy is in itself offensive or defensive. (p.34)


Internal consistency

Slessor establishes the limits of his theory from the outset. The focus of the work is on the employment of air power in support of a land campaign. Through limiting his theory in this way, Slessor is able to acknowledge that there are other roles for air power that are independent of support to land forces, but that these are outside the scope of his work. He remains on theme throughout, using different examples as demonstrations of the points he is making.
Slessor ties his theory of air power employment to the broader topic of military operations by commencing the first chapter with a quote from the Field Service Regulations. He draws on the FSR throughout, particularly in relation to the principles of war listed in that publication (which are drawn directly from Fuller). In this way, Slessor’s theory is essentially nested into broader military theory.

External Validity and Importance

Slessor also uses a “Get Out of Jail Free” card throughout the work stating that a lot of the concepts and ideas he proposes will be context dependent.

  • And we must beware of making a fetish of what is really a sound general rule; it would be thoroughly unwise to get into the habit of always sending fighters in company with bomber formations, but on the other hand close escorts are by no means necessarily vicious, and in fact are often essential. Each case must be examined on its merits and decided in the light of common sense. (p.46)

In relation to anticipation of future events, Slessor states in the conclusion that the uncertainty of future development makes it difficult to predict what will happen, and that his theory may be invalidated by advances.

  • Prophecy is notoriously a hazardous occupation; and this review of air action in land warfare can be little more than a tentative groping after truth. The writer has tried to abstain from the role of advocate, and to confine himself to a reasoned and impartial examination of the case for air power. The march of events may prove him wrong—some new development may enormously enhance the power of the defence in the air, or the efficacy of passive defences from the ground; something as yet quite untried, some ray or some equivalent of the mine- fields of naval warfare, may upset our calculations; at least it may be found that we have in some respects overstated, in others underestimated, the influence of air power on armies. (p.214)
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