Only one factor among many

This is a fascinating book on a fascinating subject, written by a master of his craft as a military historian. Sir John Keegan’s declared purpose is to answer a simple question: ‘How useful is intelligence in war?’ The answer he gives is that, however useful intelligence is in disclosing the enemy’s intentions, strengths and weaknesses, wars are won not by knowledge but by brute force in battle. The modern fad to give primacy to knowledge he rejects as misleading. Addicts of spy fiction will be disappointed. Spies rarely supply relevant information in time for it to be of use. This book is not cloak and dagger stuff but a superbly researched series of case studies on the use of intelligence in war from the 18th century to the present war against terrorism.

Keegan’s first case study is Nelson’s 73 weeks’ chase, backwards and forwards across the Mediterranean, of Napoleon’s fleet in 1798. He operated in the days of sail when ‘the sea was an area of the unknown’ and discovery of the enemy dependent upon sight. On scraps of information, he came to the conclusion that the French fleet would make for Egypt. But with imperfect intelligence he made false guesses as to its route. Having found his enemy it was his ‘killer instinct’ that gave him, in the Battle of the Nile (6 August 1798), ‘a crushing victory never exceeded during the days of sailing-ship warfare’.

Nelson’s difficulties, dependent as he was on sight from a topmast, would have been lessened had he possessed the technical triumphs of the post-electronic age: the telegraph, the radio and aerial photography and today’s satellites. Keegan’s account of the successes of Bletchley Park’s Code and Cipher School in cracking the fiendishly coded messages sent by the Enigma machine is of absorbing interest.