Chapter V: The Battle Plan

My plan for the impending battle involved the employment of four Divisions in the actual assault, with one Division in reserve. The Reserve Division was to be available for use in one of two ways; either as a reserve of fresh troops to exploit any successes gained upon the first day, or else to take over and hold defensively the ground won, if the assaulting Divisions should have become too exhausted to be relied upon for successful resistance to a counter-attack in force.

The frontage allotted to the Corps was 7,000 yards, and this extent of front accommodated itself naturally to the employment of two first-line Divisions, each on a 3,500 yard front, each Division having two Brigades in the front line, with one Brigade in reserve.

As four Divisions were available to me for immediate use in the battle, I decided to undertake, for the first time in the war, on so comprehensive a scale, the tactical expedient of a "leapfrog" by Divisions over each other.

This term had, long before, passed into the homely phraseology of the war, in order to describe a procedure by which one body of troops, having reached its objective, was there halted, as at a completed task, while a second body of troops, of similar order of importance, but under an entirely separate Commander, advanced over the ground won, reached the foremost battle line, took over the tactical responsibility for the fighting front, and after a prescribed interval of time continued the advance to a further and more distant objective.

This conception of an advance by a process of "leapfrog" had been evolved early in 1917 in connection with a method of assault on successive lines of trenches. It was intended at the outset to be applied only to very small bodies of infantry, such as platoons. A normal battle plan for a company of infantry of four platoons was for the first two platoons to capture and hold the front line trench, while the next two following platoons would leap over this trench and over the troops who had gained it, and then pass beyond to the capture of the second, or support trench. The method was used, for the first time, on such a modest scale, at the battle of Messines, in June, 1917, and later on in the same year was adopted for bodies as large even as Battalions, in the fighting for the Broodseinde and Passchendaele heights.

But on no previous occasion had such a principle been applied to whole Divisions. It is true that at the battle of Messines, the Fourth Australian Division passed through the New Zealand Division after the latter had completed the capture of the main Messines ridge, but this was really exploitation, undertaken in order to take advantage of the temporary confusion of the enemy, and for the purpose of gaining ground upon the eastern slopes of the captured ridge. It was not a movement which was really part of the main assault, and it was confined to a single Division.

On the present occasion my purpose was to carry out a clear and definite process of "leapfrogging," not only simultaneously by two Divisions side by side, but also as an essential part of the time-table programme for the main battle, and before the exploitation stage of the fighting was timed to be reached. It was, undeniably, a daring proposal, involving very definite risks, enormously increasing the labour of preparation and the mass of detailed precautions which had to be undertaken in order to obviate the possibility of great confusion.

The preparations necessary for a single Division proposing to advance alone, to a prescribed distance, over country much of which was usually visible to us from our front line, are sufficiently complex, relating as they do, not only to the establishment of numerous protected headquarters for Brigades and Battalions, of miles upon miles of buried and ground cables, of dumps of all kinds of supplies, and of dressing stations and medical aid posts; but also to the disposition, in concealed positions, of all the assaulting units, down to the smallest of them, of Infantry Engineers and Pioneers. All these preparations assume a tenfold complexity when a second Division has to make arrangements exactly similar in character, variety and extent, using exactly the same territory for the purpose and at the same time, and planning to advance over more distant country, entirely beyond visual range and preliminary reconnaissance.

The project also involved a much greater crowding of troops into the areas immediately behind our line of departure, and, therefore, enormously increased the risk of premature detection by the enemy, both from ground and from air observation, of unusual movement and of other symptoms which presaged the possibility of an attack by us. The plan also necessitated the closest possible co-ordination of effort, and mutual sympathy and understanding, between the Commanders and Staffs of the twin Divisions having a common jurisdiction over one and the same area of preparation, and one and the same battle front. This was a degree of co-operation which could not have been looked for unless the personnel concerned had already established, from long and close association with each other, the most cordial personal relations. And dominating all other difficulties were those involved in the proposal to execute this difficult and untried operation of a Divisional leapfrog, not singly but in a duplex manner, necessitating the assurance of exactly similar simultaneous action, similarly timed in every stage, both before and during battle, by each of two separate pairs of Divisions.

These threatening difficulties were surely formidable enough, but I knew that I could rely upon the goodwill of the Divisions towards each other, and upon the loyal support of them all. This seemed to me to justify the attempt, and to minimize the risks; having regard above all else to the results which I stood to gain if the operation could be executed as planned.

On no previous occasion in the war had an attempt ever been made to effect a penetration into the enemy's defences at the first blow, and on the first day, greater than a mile or two. Rarely had any previous set-piece attack succeeded in reaching the enemy's line of field-guns. The result had been that the bulk of his Artillery had been withdrawn at his leisure, and his losses had been confined to a few hundred acres of shattered territory. But the task I had set myself was not only to reach, at the first onslaught, the whole of the enemy's Artillery positions, but greatly to overrun them with a view to obliterating, by destruction or capture, the whole of his defensive organizations and the whole of the fighting resources which they contained, along the full extent of my Corps front.

To achieve this object I prepared my plans upon the basis of a total advance, on the first day, of not less than 9,000 yards. This was to be divided into three separate stages, as follows:

Phase A--Set-piece attack with barrage, 3,000 yards.
Phase B--Open-warfare advance, 4,500 "
Phase C--Exploitation, 1,500 "
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Total distance to final objective, 9,000 yards.
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The opening phase involved no novel or unusual features so far as the infantry were concerned, and was conceived on lines with which the fighting of 1917 had familiarized me, modified further by the accumulated experience gained from earlier mistakes in the technical details of such an enterprise. The recent battle of Hamel became the model for this phase, the conditions of that battle being now reproduced on a much enlarged scale.

But there was one very important feature which distinguished the present undertaking from the battles of Messines and Broodseinde, and that was in regard to the frontage allotted for attack to a single Division. At Messines, the Divisional battle front was 2,000 yards; in the third battle of Ypres it differed but little from the same standard. For the present battle, I adopted a battle front of two miles for each assaulting Division, or a mile for each of the four assaulting Brigades.

This innovation seemed to me to be justified by four principal factors. The first of these was that the weather, which was dry, and the state of the ground, which was hard, made the "going" easy and the stress upon the infantry comparatively light. Next, the condition of the enemy's defensive works was undeveloped and stagnant, as clearly disclosed by the air photographs which the Corps Air Squadron produced in great numbers on every fine day. No doubt this was due to the encroachments we had made on his forward works during the fighting at Hamel and in the remaining weeks of July. Thirdly, the powerful assistance anticipated from a contingent of four Battalions of Tanks which General Rawlinson had arranged to place under my orders led me to estimate that I might greatly reduce the number of men per yard of front. Lastly, the plan was justified by the known distribution of the enemy's infantry and guns along the frontage under attack. For all these reasons, I felt prepared to impose on the infantry a task which, computed solely upon the factor of frontage, was more than twice that demanded by me on any previous occasion.

At the same time, so extended a frontage involved the employment of a much higher ratio of barrage artillery to the number of battalions of Infantry actually engaged. Success depended more upon the efficiency of the fire power of the barrage than upon any other factor, and I could not afford to incur any risk by weakening the density of the barrage. For this reason, I adhered to the standard which previous experience of several major battles and many minor raids had shown to be adequate for covering the assaulting infantry, and for keeping down the enemy's fire. This standard never fluctuated widely from one field-gun per twenty yards of front, and involved the employment, on this occasion, of some 432 field-guns in the barrage alone. This result could not have been achieved if the Fourth Army authorities had not seen their way to place at my disposal five additional Brigades of Field Artillery over and above the thirteen Australian Brigades which formed a permanent part of the whole Artillery of the Corps.

Phase A, as already stated, involved a penetration of 3,000 yards, and the objective line for this phase, which came to be known as the "green" line (from the colour employed to delineate it upon all the fighting maps propounded by the Corps), was chosen, after an exhaustive study of all aeroplane photographs, and of the results of numerous observations, by many diverse means, of the locations of the enemy's Artillery, so as to make certain that during this phase the whole mass of the enemy's forward Artillery would be overrun, and captured or put out of action.

The green line was, in fact, located along the crest of the spur running north-easterly from Lamotte-en-Santerre in the direction of Cerisy-Gailly, with the object of carrying the battle well to the east of the Cerisy valley, in which large numbers of the enemy's guns had been definitely located. This would give us, by the capture of this valley, suitable concealed positions in which the Infantry destined for Phase B could rest for a short "breather;" and would land the Infantry of the original assault in a position from which they could detect and forestall any attempt on the part of the enemy to launch a counter-attack before the time for the opening of Phase B had arrived.

The task of executing Phase A of the battle fell to the Second and Third Australian Divisions, in that order from south to north, the southern flank of the Second Division resting upon the main railway line from Amiens to Péronne, and being there in contact with the Canadian Corps, under General Currie. The northern flank of the Third Division rested on the River Somme, and was there in contact with the Third British Corps under General Butler, while the inter-divisional boundary was at the southern edge of the Bois-d'Accroche.

These two Divisions were the line Divisions during the period immediately preceding the battle, and had been holding the line each with two Brigades in line and one Brigade in support. Three days prior to the battle, however, it was arranged that each Division should hold its front with only one Brigade, thereby making available two Brigades each for the actual carrying out of Phase A of the attack. These assaulting Brigades were the 7th, 5th, 9th and 11th, in that order from south to north, each Brigade having its due allotment of Tanks and machine guns, etc.

The total estimated time for the completion of Phase A was to be 143 minutes after the opening of the barrage at "zero" hour; and there was then to be a pause of 100 minutes to allow time for the advance and deployment into battle order of the succeeding two Divisions, who were to carry out the process of "leapfrogging" and to execute Phases B and C of the battle.

The planning of Phase B, or the advance from the "green" to the "red" line, involved a totally different tactical conception and the adoption of a type of warfare which had almost entirely disappeared from the Western theatre of war since those far-off days in the late autumn of 1914, when the German Army first dug itself in, in France and Belgium, and committed both combatants to the prolonged agony of over three years of stationary warfare. I allude to the moving battle, or as it is called in text-book language, "open warfare;" a type of fighting in which few of the British Forces formed since the original Expeditionary Force had any experience except on the manoeuvre ground under peace conditions--a disability which applied equally to the Australian troops. Confident, however, in their adaptability and in their power of initiative under novel conditions, I did not hesitate to prescribe, for this second phase of the battle, the adoption of the principles and methods of open warfare.

In two very important respects in particular, this type of fighting involved conditions to which the troops had not been accustomed, and under which they had no previous experience in battle. In trench warfare, and in a deliberate attack on entrenched defences, the positions of all headquarters, medical aid posts, supply dumps and signal stations remained fixed and immovable. The whole of the internal communications by telegraph and telephone could, therefore, be completely installed beforehand, down to the last detail, and the transmission of all messages, reports, orders and instructions, during the course of the battle, was rapid and assured. But in a moving battle no such comprehensive or stable signalling arrangements are possible, and reliance must be placed upon the much slower and much more uncertain methods of transmission by flag and lamp signalling, by dispatch riders, pigeons and runners.

Divisional Headquarters would, therefore, almost as soon as the battle commenced, fall out of touch with Brigades, and they in turn with their Battalions; information as to the actual situation at the fighting front would travel slowly, and would reach those responsible for making consequential decisions often long after an entire alteration in the situation had removed the need for action. Thus, a greatly enhanced responsibility would come to be imposed upon subordinate leaders to decide for themselves, without waiting for guidance or orders from higher authority, and to grasp the initiative by taking all possible action on the spot in the light of the circumstances and situation of the moment.

Again, the nature of the Artillery action is, in the moving battle, fundamentally different from that which prevails during trench warfare. To begin with, only that portion of the Artillery which is in the strictest sense mobile can participate to any extent in open warfare. The employment of Artillery is, therefore, confined to a few and to the smaller natures of Ordnance, namely, the 18-pounder field-gun, the 4½-inch field howitzer and the 60-pounder, which are all horse drawn and which are capable of being moved off the roads and across all but the most broken country. Heavier guns, from 6-inch upwards, are in practice confined to roads, and are too slow and cumbersome to keep pace with the Infantry. The Artillery fire action is also intrinsically different, because the guns can be sighted directly upon their targets, while in trench warfare they are always laid by indirect methods, with the use of the map and compass, and without observation, at any rate by the crew of the gun, of the objects fired at.

The decision which I had to take of carrying out the second phase of this great battle on the principles of open warfare was, therefore, one which also involved a certain element of risk. But it was a risk which I felt justified in taking, in spite of the fact that the German High Command had more than once expressed itself in contemptuous terms of the capacity of any British troops successfully to undertake any operation of open warfare. My justification lay primarily in my confidence in the ability of the subordinate commanders and troops to work satisfactorily under these novel conditions--a confidence which the event abundantly justified. But I was placed in the position of having either to accept this risk, or else abandon altogether the project of a quite unprecedented penetration of enemy country to be completed on the first day. It would have been clearly impossible to continue the advance beyond the green line without an interval of at least forty-eight hours, which would have been necessary to enable the Artillery to be redisposed for barrage fire in forward positions and provided with the necessary supplies of ammunition for such a purpose.

The Divisions which were told off to carry out the "leapfrog" enterprise and to execute Phase B of the battle were the Fifth Australian Division on the south and the Fourth Australian Division on the north, the outer flanks of the attack remaining as before, _i.e._, the Péronne Railway on the south and the River Somme on the north. Each of these Divisions was directed to deploy, on its own frontage, two Infantry Brigades. Its third Brigade was to be kept intact and to advance during Phase B at some distance behind, as a support to the fighting line, and to be employed in the subsequent phase, if it were found that Phase B could be completed without calling upon this spare Brigade. The actual dispositions of the Brigades finally proposed by the respective Divisional Commanders and approved by me brought about the arrangement that the four first-line mobile Infantry Brigades were successively, from south to north, the 15th, 8th, 12th and 4th, while the 14th and 1st Brigades followed as supports in a second line.

To each of these Infantry Brigades I allotted a Brigade of Field Artillery, to be employed under the direct orders of the Infantry Brigade Commander, and, in addition, three Artillery Brigades as well as one Battery of 60-pounders, to each Divisional Commander. As my resources in Artillery were not unlimited, the twelve Artillery Brigades, so disposed of, were necessarily drawn from the original eighteen Brigades which were to fire the covering Artillery barrage for Phase A of the battle. The orders to that portion of the Field Artillery which was to become mobile in pursuance of this plan, accordingly, were that immediately upon the completion of their original tasks, by the capture of the green line, they were to "pull out of the barrage."

This meant, in effect, that all the teams, limbers, battery wagons, and ammunition wagons of these twelve Brigades, waiting in their wagon lines far in rear, fully harnessed up and hooked in at the opening of the battle, had to advance during the progress of the first phase, so as to reach their guns just at the right time, but no earlier, to enable these guns to be limbered up, and the batteries to become completely mobile in order to join and advance with the Infantry of the second phase.

This was an operation which required the greatest nicety in timing, and the greatest accuracy in execution. No Australian Artillery had ever previously undertaken such an operation, except perhaps on the manoeuvre ground, and then only on the very limited scale of a Brigade or two at a time. That this rapid transition from the completely stationary to the completely mobile battle was carried out, during the very crisis of a great engagement, without the slightest hitch, and with only the trifling loss of two or three gun horse teams from shell fire, reflects the very highest credit upon every officer and man of the Australian Field Artillery.

The open warfare Infantry Brigades were also to be provided, out of their own divisional resources, each with a Company of Engineers, a Company of Machine Guns, a Field Ambulance, and a detachment of Pioneers, so that, in the most complete sense, they became a Brigade Group of all arms, capable of dealing, out of their own resources and on their own ground, with any situation that might arise during their advance of nearly three miles from the green to the red line. A detachment of nine tanks completed the fighting equipment of each of the four front line Brigades destined to capture the red line.

I must now briefly describe the nature of Phase C, the third and last stage in this ambitious and complex battle programme. This phase was to consist of "exploitation," which implies that it was a provisional preparation, which was to be carried out only if complete success attended the two preceding phases. The objective of Phase C was the "blue" line, which I had located about one mile to the east of the red line, along a system of old French trenches extending from the river at a point near Méricourt, and running southerly to the railway at a point a little to the south-east of Harbonnières. This line gave promise of furnishing a good defensive position in which to deal with any possible counter-attack. It also gave a good line of departure for subsequent operations, and provided ideal artillery positions in a series of valleys, running parallel and a little to the west of the line itself.

The troops earmarked for this Exploitation Phase were the two second line Brigades of the two Divisions which were to capture the red line, namely, the 14th and 1st Brigades, and the orders to the Divisional Commanders were that if the red line was reached without mishap, without undue loss of time, and without involving the Reserve Brigades, but not otherwise, these Reserve Brigades were to push on with the utmost determination to secure and hold the blue line until such time as they could be reinforced.

Each of these exploitation Brigades was equipped similarly to the red line Brigades in all respects except that they were provided with a special contingent of 18 Mark V. (Star) Tanks of the very latest design. These differed from the Mark V. Tank employed at Hamel and in the other stages of the present operation, in that they were longer and had sufficient internal space to carry, as passengers, over and above their own crews, two complete infantry Lewis gun detachments each. It was expected that this infantry fire power, added to the fire power from the machine guns carried by these 36 Tanks themselves and operated by the Tank crews, would go far to compensate for the somewhat attenuated line of probably tired Infantry spread in two Brigades over an ultimate frontage of over 10,000 yards.

No definite time-table was laid down for the closing phases of the battle, except for the regulation of the times when our Heavy Artillery should "lift off" designated targets--such as villages, farms, and known gun positions--and lengthen its range so as not to obstruct the further advance of our own Infantry. But it was estimated that, from the opening of the battle, the green line would be reached in two and a half hours, the red line in six hours, and the blue line in eight hours. As the battle was to open at the first streak of dawn, it would, if all went well, be completed according to plan by about midday.

In every battle plan, whether great or small, it is necessary first of all to map out the whole of the intended action of the Infantry, at any rate on the general lines indicated above. When that has been done the next step is to work backwards, and to test the feasibility of each body of infantry being able to reach its allotted point of departure, punctually, without undue stress on the troops, and without crossing or impeding the line of movement of any other body of infantry. It is often necessary to test minutely, by reference to calculations of time and space, more than one alternative plan for marshalling the Infantry prior to battle, and for the successive movements, day by day, and from point to point, of every battalion engaged.

The present case was no exception, and, indeed, presented quite special difficulties. The whole of the area for a depth of many thousands of yards behind our then front line was open rolling country, devoid of any cover, and (except in the actual valley of the Somme) with every village, hamlet, farmhouse, factory and wood obliterated. The plan involved the assembly, in this confined area, fully exposed by day to the view of any inquisitive enemy aircraft, of no less than 45 Infantry Battalions, with all their paraphernalia of war; not to speak of our 600 guns of all calibres, their wagon lines, horse lines and motor parks, together with Engineers, Pioneers, Tanks, Medical and Supply Units amounting to tens of thousands of men and animals.

A new factor which, however, ultimately controlled the final decision which I had to make as to the nature of the dispositions prior to battle, lay in the consideration of the maximum distances which would have to be covered by the foot soldiers in such a far-flung battle. I had little difficulty in coming to the conclusion that the obvious and normal arrangement was on this occasion a totally wrong arrangement. If the assaulting Brigades had been arranged, from front to rear, in their assembly areas prior to battle, in the same order as that in which they would have to come into action, this would have involved that the individual man, who was to be required to march and fight his way furthest into enemy country, and, therefore, was to be the last to enter the fight, would also be called upon to march furthest from his rearmost position of assembly before even reaching the battle zone. The maximum distance to be traversed on the day of battle by infantry would have amounted, according to such a plan, to over ten miles. While this is an easy day's march on a good road, under tranquil conditions, it would have been an altogether unreasonable demand upon any infantryman during the stress and nervous excitement of battle. It would have been courting a breakdown from over-fatigue, among the very troops upon whom I had to rely most to defend the captured territory against any serious enemy reaction.

I therefore adopted the not very obvious course of completely reversing the normal procedure, and of disposing the Brigades in depth, from front to rear, in exactly the _reverse_ of the order in which, in point of time, they would enter the battle.

The following represents, diagrammatically, the disposition of all twelve Brigades after having been fully _deployed_ in the actual course of the battle:

^ (4th Division) | (5th Division)
| Direction 4 -- 12 | 8 -- 15
| of North 1 Inter- 14 South
| enemy. (3rd Division) Divisional (2nd Division)
| 11 -- 9 Boundary. 5 -- 7
| | Our front line
|----------------------------------+---------------------------------
| | before battle
| 10 (in our trenches) | 6 (in our trenches)

The next diagram shows how the twelve Brigades were disposed while Phase A of the battle was in progress, and before the second Phase had begun:

(3rd Division) | (2nd Division)
11 -- 9 | 5 -- 7
Inter- Our front line
--------------------------------Divisional---------------------------
Boundary. before battle
10 (in our trenches) | 6 (in our trenches)
(4th Division) | (5th Division)
4 -- 12 | 8 -- 15
1 | 14

But the following diagram represents, in a similar manner, the order of disposition of the same Brigades, in the territory under our own occupation, immediately _prior_ to the battle:

^ (3rd Division) | (2nd Division)
| | Our front line
|-----------------------------------+---------------------------------
| Direction Inter- before battle
| of 10 (in our trenches) Divisional 6 (in our trenches)
| enemy. (4th Division) Boundary. (5th Division)
| 4 -- 12 | 8 -- 15
| North 1 | 14 South
| (3rd Division) | (2nd Division)
| 11 -- 9 | 5 -- 7

A little consideration will show that this apparently paradoxical procedure brought about the desired result of more nearly equalizing the stress upon the whole of the Infantry engaged, in point, at least, of the maximum distance to be traversed in the day's operations. But it produced something else, also, of much greater concern, which was that the scheme involved a leapfrogging of Divisions during the approach march into the battle, in addition to a second leapfrogging, to which I was already committed, to occur at a later stage during the battle itself.

Thus I was confronted with the dilemma that the only scheme of disposition which promised success for the subsequent battle was also that scheme which made the greatest possible demands upon the intelligence of the troops and the sympathetic, loyal and efficient co-operation of my own Corps Staff, and those of the Commanders acting under me. Influenced once again by the confidence which I felt in my whole command, I did not hesitate to increase the complexity of the plans for the Infantry action by calling upon the four Divisions to execute a manoeuvre which is unique in the history of war, namely, a "double leapfrog," simultaneously carried out by two separate pairs of Divisions, operating side by side. The first leap was to take place during the approach to the battle, the second during the progress of the battle itself.

This expedient, which I finally decided to adopt, in spite of the dangers involved in its complexity and in the absence of any precedent, was, however, as logical analysis and the event itself proved, the very keynote of the success of the entire project. The whole plan, thanks to an intelligent interpretation by all Commanders and Staffs concerned, worked like a well-oiled machine, with smoothness, precision and punctuality, and achieved to the fullest extent the advantages aimed at.

On the one hand, the stress upon the troops was reduced to a minimum. By the reduction of physical fatigue, it conserved the energies of whole Divisions in a manner which permitted of their speedy re-employment in subsequent decisive operations. And on the other hand, by the great depth of penetration which it rendered possible, it ensured a victory which amounted to so crushing a blow to the enemy that its momentum hurled him into a retrograde movement, not only along the whole front under attack, but also for many miles on either flank. This recoil he was never able to arrest, as we followed up our victory by blow after blow delivered while he was still reeling from the effects of the first onslaught of August 8th.

But, so far, I have written of the Infantry plan only; and much remains to be told of the simultaneous action designed to be taken by all the other arms, which rendered possible and emphasized the success of the Infantry. No one can rival me in my admiration for the transcendant military virtues of the Australian Infantryman, for his bravery, his battle discipline, his absolute reliability, his individual resource, his initiative and endurance. But I had formed the theory that the true rôle of the Infantry was not to expend itself upon heroic physical effort, nor to wither away under merciless machine-gun fire, nor to impale itself on hostile bayonets, nor to tear itself to pieces in hostile entanglements--(I am thinking of Pozières and Stormy Trench and Bullecourt, and other bloody fields)--but, on the contrary, to advance under the maximum possible protection of the maximum possible array of mechanical resources, in the form of guns, machine guns, tanks, mortars and aeroplanes; to advance with as little impediment as possible; to be relieved as far as possible of the obligation to _fight_ their way forward; to march, resolutely, regardless of the din and tumult of battle, to the appointed goal; and there to hold and defend the territory gained; and to gather in the form of prisoners, guns and stores, the fruits of victory.

It is my purpose, therefore, to emphasize particularly the extent to which this theory was realized in the battle under review, by the achievement of a great and decisive victory at a trifling cost. That result was due primarily to the very ample resources in mechanical aids which the foresight and confidence of the Fourth Army Commander, General Rawlinson, entrusted to me; but it was due partly, also, to the manner in which those resources were employed. And that is why I shall attempt to describe the remainder of the Corps plan.