Unlike standard coordinate converters that use mathematical projection formulas, this tool provides a true-to-map conversion whenever a digitised wartime map for the area is available. This ensures the result matches the WW2 GSGS 4250 mapping used by British and Allied forces in Normandy and Northwest Europe. Where no georeferenced sheet exists, the converter falls back to a reliable projection-based conversion, still giving accurate latitude/longitude values.
By combining Google Maps integration with overlays of original WW2 cartography, the converter offers both modern geographic precision and historical context. It is designed to be user-friendly, guiding you to select the correct two-letter grid prefix and helping you interpret references exactly as they appear in wartime documents.
Currently the converter only supports Lambert Zone 1, the grid references need to be entered with the 2 character prefix followed by 4 or 6 numbers for example vT9081 or vT902818.
If working with co-ordinates in the Normandy area you will most likely need the prefix vT unless the first number is a low one and your working East of Caen where vU is likely needed. A utility to help with the grid prefix will be added soon.
In the British Modified System (BMS), used on many WW2 maps of Northwest Europe, the grid is organised into large squares of 500 kilometres per side, each identified by a single letter. These 500 km squares are then divided into 25 smaller squares of 100 kilometres per side, lettered from A to Z (with the letter I omitted to avoid confusion).
Each 100 km square is referenced by combining the two letters — one from the larger 500 km square and one from its 100 km subdivision. For example, the reference vZ identifies the 100 km square “Z” within the larger 500 km square “v.” Within these squares, numbers are added (eastings and northings) to give precise grid references, which could pinpoint positions on wartime maps to within metres.