This map follows 4th Field Squadron, Royal Engineers — the divisional engineer unit of the 7th Armoured Division — from the opening of Operation Compass in December 1940 through its service in the besieged Tobruk garrison in 1941. Markers cover the capture of Italian positions during the advance, the defensive engineering works built inside the Tobruk perimeter, and the supply routes the squadron helped maintain.
Dates, locations and the squadron's order-of-battle movements (its service with 7th Armoured Division through Compass, its attachment to 2nd Armoured Division on 24 March 1941, and its entry into the Tobruk garrison on 8 April 1941) draw on the research file "A Sapper's Story — 4th Field Squadron, Royal Engineers, North Africa Research," cross-checked against the Tobruk Fortress Order of Battle and standard published campaign histories (Wikipedia, historyofwar.org, the Australian War Memorial, and unit-history sites cited throughout).
Where a milestone's engineering detail is documented at the level of the wider 7th Armoured Division or the Tobruk garrison as a whole, rather than named specifically to 4th Field Squadron, this is flagged in that milestone's "note on sourcing." A few perimeter coordinates inside Tobruk (Ras el Medauar, Fort Pilastrino, Twin Pimples) are approximate, as no precisely surveyed public coordinate could be confirmed for them.