"An army which undertakes the conquest of a country has its two wings either resting on neutral territories or upon great natural obstacles, such as rivers or chains of mountains. It happens in some cases that only the wing is so supported, and in others that both are exposed.
In the first instance cited, viz., where both wings are protected, a general has only to guard against being penetrated in front. In the second, where one wing only is supported, he should rest upon the supported wing. In the the third, where both wings are exposed, he should depend upon a central formation, and never allow the different corps under his command to depart from this; for it be difficult to contend with the disadvantage of having two flanks exposed, the inconvenience is doubled by having four, tripled if their be six; that is to say, if the army is divided into two or three different corps. In the first instance then, as above quoted, the line of operation may tend indifferently to the right or to the left. In the second, it should be directed towards the wing in support. In the third, it should be perpendicular to the centre of the army's line of march. But in all these cases it is necessary every five or six days to have a strong post, or an entrenched position, upon the line of march, in order to collect stores and provisions, to organise convoys, to form a centre of movement, and establish a point of defence, to shorten the line of operations."
As Chandler points out in his comment on this general principle of operations, the choice of where to position an army's line of communication based on the situation it finds itself in is as important a consideration today as it was in Napoleon's time.
The idea was well illustrated with Napoleon's own invasion of Spain in 1808 where his centre of operations was established at the fortified city of Bayonne, close to the border of Spain in south west France and with the access into Spain flanked by the Bay of Biscay. The area around Bilbao up to the north coast was quickly secured against Blake's Spanish Army of the Left, with the corps of Victor (I Corps), Lefebvre (IV Corps) and Soult (II Corps). Thus with his wing securely placed, Napoleon was able to manoeuvre against Castanos and his Spanish Army of the Centre, quickly taking Burgos and swinging Ney (VI Corps) in towards Soria and pinning and defeating the Spanish at Tudela (between Zaragoza and Logrono on the River Ebro) with Moncey (III Corps) holding the French side of the Ebro. This opened up the route to Madrid with a new forward base centred on Burgos.
|Map illustrating the opening moves of Napoleon's invasion in November - December 1808 - West Point Dept of History Map|
With his northern wing securely anchored and Madrid taken Napoleon was very well placed to swing his reserve north from Madrid as he attempted to encircle Sir John Moore as he approached Burgos via Salamanca. Only the fortuitous capture of French orders revealing the plan, obtained from Spanish partisans alerted Moore in good time to enable him to get a days march on the fast approaching French forces and commence his retreat towards Lugo and Corunna.
Moore was correct in selecting Burgos as a good point to strike, as it was the main bastion on the French line of communication (L.O.C.) back to Bayonne and its taking would have severely embarrassed Napoleon's forces in and around Madrid; however the French forces in the area were the anchor to the whole invasion with the rest of the army "resting" upon its supported wing. In addition when Moore made his move, the Spanish forces he hoped to cooperate with were no longer forces in being and the British army would have been putting their "head in the noose" with a continued advance.
Chandler highlights Napoleon's point that the security of the LOC is only enhanced by having it perpendicular to the armies line of march and clearly Napoleon was operating on this principle with his route from Burgos to Bayonne and on down to Madrid. The principle of placing depots and strong points at regular intervals would also be practised by Wellington during his own counter advances into Spain from Lisbon and Ciudad-Rodrigo, however Wellington took the principle one stage further by utilising the sea power of the Royal Navy to help him relocate his centre of operations from Lisbon to Santander in 1813 as he pursued French forces beyond the Spanish border, illustrating the flexibility of a naval power over a continental power.