Working with "Modified British System" grid references in Italy

Allied forces operating in Italy used WW2 used a grid-reference system that might be new to you. It is called the "Modified British Grid System". There are two separate grids - North and South - that cover the respective regions of Italy. Full grid references consist of two letters followed by six numbers aB123456. This is very similar to how grid references work on Ordnance Survey maps.

This website has lots of diagrams and a tool to turn grid references in to lat/long. This proj string will help you convert grid references in QGIS. Together these tools are helpful if you wish to locate the grid reference but do not possess a copy of the relevant WW2 map sheet.

Authors of historical documents regularly truncated the grid references for convenience. It is common to find references that are incomplete and missing letters or numbers.

Any context that you have is very helpful. Knowing just the general area or even as little as that the location must be on land, or that it is on the north or south grid is helpful.

If numbers are missing: Six digits are only required if the reference is accurate to a 100m x 100m square. If you have four digits you will be able to identify a 1km x 1km square. If you only have two digits you will only be able to identify a 10km x 10km square. You must have an even number of digits.

If one letter is missing: Typically it's the first letter that's missing. There are also fewer first letters to go through making it easier. Either way - go through each possibility for the missing letter (potentially in both grids), and work out the possible locations and eliminate the impossible ones (for example if you know you're looking for a village, discard the possibilities that end up in the sea). This is not as much work as it seems as most of the eliminations can be done visually using a diagram of the grid - for example if you are looking for H1234 in Sicily, you know it has to be wH1234.

If both letters are missing: The same as above but you will need to heavily rely on context if you wish to avoid coming up with lots of possibilities. For example if you're looking for 1234 in Sicily you only have to look at wA, wB, wC, wD, wF, wG, wH, wJ and wN.