The right answer is: it was short but difficult series of battles.
Allied forces and Nazi Germany faced each other in a series of battles in Normandy, North France, known as “The Invasion of Normandy”. It lasted, more and less, a month and a half between June and July 1944, but it was important for the final result of the Second World War. It was difficult for the Allied because the Nazi had built large defenses and fortifications in the coast line that were able to broke at the end, provoking a retreat to the East from the Nazi force.
