An American military historian now working in Australia wrote of the British Army in WWI that they had an ethos rather than a doctrine: embedded behaviors from the collective memory of the regiments. No, the British Army didn't have a COIN doctrine going into their participation in the Iraq War even after decades of hands-on "war among the people" or COIN in N' Ireland. I suspect it is different to find a serving officer or long-service NCO who has not served multiple rotations in N' Ireland (like the US Army and Marines now with multiple tours in a GWOT theater). This embedded, tacit knowledge is perhaps more valuable than all the doctrine written. Such knowledge didn't keep them from their issues in Southern Iraq I suspect. The internal BA study on their historical experiences and learning about COIN did not paint a pretty picture.

One reason the joint US COIN manual had little new in it was that the old knowledge was largely unknown. Even in army special forces in the '80s and '90s I found there was very little in the way of historical discussion possible about anything other than Vietnam or El Salvador because there was almost no venue for professional, serious study. It is interesting that McMasters and Petreaus both did Vietnam War dissertations outside of the military during their advanced civil schooling. The only officer, at the risk of injecting an anecdote, I recall a historical conversation with about small wars with was the now-USASOC commander when he was a battalion XO. We discussed SF and the Montagnards in VN.

The TRADOC history of the period immediately following the Vietnam War makes pretty clear - as does Conrad Crane's monograph for SSI - that the army seized upon the 1973 war in the Middle East with its high intensity and combined arms requirements with notable zeal. This institutional decision - rather than studying the recent, long return from Vietnam - resembles very much the British Army's decision to return to real soldiering on the frontiers of the Empire in the 1930s rather then study WWI for knowledge.