are readily accepted, while contrary reports have to reach a higher threshold. This is not only perfectly understandable, it is the way perception normally operates. But in the intelligence world in which data are scanty, may be deliberately intended to confuse and may sometimes be more inadequate than can be appreciated, normal rules do not apply.
In the UK, assessment is usually explicitly described as ‘all-source’. Given the imperfections of intelligence, it is vital that every scrap of evidence be examined, from the most secret sources through confidential diplomatic reports to openly published data. Intelligence cannot be checked too often. Corroboration is always important but seldom simple, particularly in the case of intelligence on ‘hard targets’9 such as nuclear, biological or chemical weapons programmes or proliferation networks. The simple fact of having apparently coincident reports from multiple types of intelligence sources is not in itself enough. Although reports from different sources may say the same thing, they may not necessarily confirm one another. Is a human intelligence report that a factory has been put into operation confirmed by imagery showing trucks moving around it? Or are both merely based on the same thing – observation of physical external activity? Reporting of different but mutually consistent activities can be complementary. This can build up knowledge to produce a picture which is more than the simple sum of the parts. But it may be false, if there is no link between the pieces other than the attractiveness of the resulting picture. Complementary information is not necessarily confirmatory information.
Multiple sources may conflict, and common sense has to be used in evaluation. A dozen captured soldiers may have provided mutually consistent and supportive reports about the availability of chemical weapons to their neighbouring battalion. But if these were flatly contradicted by a single report from a senior member of that battalion, which should be believed?
It is incorrect to say, as some commentators have done, that ‘single source’ intelligence is always suspect. A single photograph showing missiles on launchers, supporting a division deployed in the field, trumps any number of agent reports that missiles are not part of a division’s order of battle. During the Second World War, innumerable Allied command decisions were taken on the basis of intelligence reports from a single type of source (signals intelligence, providing decrypts of high-level German and Japanese military plans and orders), and quite often (e.g. re-routing convoys in the middle of the Atlantic) important decisions had to be taken on the basis of a single report. As before, common sense and experience are the key.
Assessment must always be aware that there may be a deeper level of reality at which apparently independent sources have a common origin. Multiple sources may have been marshalled in a deception campaign, as the Allies did in Operation Fortitude before D-Day to mislead the German High Command about the location of the landings. Although deception on so grand a scale is rare, the chance of being deceived is in inverse proportion to the number of independent sources – which, for ‘hard targets’, are few.
In a sense, almost all intelligence is conducted against ‘hard targets’. If the information were readily available, it would not be necessary to call on intelligence resources to acquire it. But within the hierarchy of intelligence activities it is inevitable, given the protection afforded to nuclear, biological and chemical weapons programmes, that they are among the hardest targets.