These notes are intended to summarize how the information is presented for the battalion defence schemes on this website. During war time, each unit of battalion upwards has to keep a War Diary and also, in its WW2 Home Defence role, produce a Defence Scheme. Sometimes these are included with the War Diary filed at the National Archives. Military Training Pamphlet No23 1939 details the contents of the ideal Defence Scheme. If the battalion War Diary lacks a Defence Scheme, it is often possible to get details of road blocks, demolitions etc at least from Brigade or Divisional War Diaries.
Defence Scheme, Military Training Pamphlet No 23
Operations Part II - The Defence, 1939
Localities in War Diaries are given in the old Cassini Grid Reference system as the Second War interrupted the switch to the modern National Grid system. The most accurate way to translate a Cassini Grid Reference to a modern grid reference is to have both maps side by side and plot a location from one to the other. This is time consuming and you also have to get hold of an old Cassini map! John Perry (Regional Historian, Issue 5, Summer 2000) summarizes a Royal Engineer’s formula for converting grid references with an accuracy of +/- 200 mtrs. Due to the large number of grid references involved this is the method I have used to convert Cassini to modern National Grid. I have then plotted localities onto copies of 1:25,000 and one inch to one mile maps dating from 1946-56. These have the advantage of showing the landscape more or less as it was during the war and also are not subject to copyright (OS maps only have a 50 yr copyright).
I believe the maps I have produced do give a good visual representation but should not be relied upon for pin-point accuracy due to the conversion formula not being 100% accurate. Having said that, most road blocks and road craters do end up being plotted on roads! In the odd occasion where they don’t, its often easy to make an educated guess as to where to plot them. However for gun positions etc I have to rely solely on the conversion. It should also be noted that boundaries drawn on the maps for company and platoon localities are illustrative only, being drawn around the places (village name or plotted converted grid reference) given for a particular unit in the Defence Scheme/War Diary.
Military Training Pamphlet No 23 – Operations Part II.- Defence, WO, 1939
Straight to the point right on time, J Perry, Regional Historian, Issue 5, 2000