By the Normandy landings in June 1944, 2 TAF had eighteen operational squadrons of Typhoon IBs, while RAF Fighter Command had a further nine. The aircraft proved itself to be the most effective RAF tactical strike aircraft, on interdiction raids against communications and transport targets deep in North Western Europe prior to the invasion and in direct support of the Allied ground forces after D-Day. A system of close liaison with the ground troops was set up by the RAF and army: RAF radio operators in vehicles equipped with VHF R/T travelled with the troops close to the front line and called up Typhoons operating in a "Cab Rank", which attacked the targets, marked for them by smoke shells fired by mortar or artillery, until they were destroyed.