In 1892 Clarke published "Fortification: Its Past Achievement, Recent Development and Future Progress". The book was influential in shaping the British view of military fortification. Clarke adhered to the 'Blue Water' school of thought which saw the Royal Navy as Britain's primary defence against invasion. Large scale permanent fortifications built in peacetime (such as the Palmerston Forts) were seen as a waste of money. Instead Clarke advocated the use of small field fortifications which could be built cheaply and rapidly, such as those based on the Twydall Profile. His view was based in part on the successful defence of Plevna in 1877 by Turkish forces using magazine-fed rifles and earthwork fortifications. Also, in 1882 following the heavy bombardment of the forts at Alexandria by the British Mediterranean Fleet, Clarke, as an engineer officer, had been given the task of assessing the damage to the forts. He found the bombardment had had very little effect on the earthwork defences with only 20 of the 300 guns having been dismounted. Returning from the Mediterranean, Clarke was appointed to a group of officers tasked with the planning of British coast defences overseas. Sydenham-Clarke's opinions on the strength of field fortifications were largely vindicated by the trench warfare of the First World War (1914–1918).