Operation Jubilee took place on 19 August 1942. The last time the British had attempted an amphibious attack on any such scale was at Gallipoli during WW1, which had been an unmitigated disaster. Churchill and the Chiefs of Staff realised that if any serious attempt of an invasion of German occupied Europe were to succeed the Allies would need to gain experience by carrying out raids such as the one planned on Dieppe.
230 Allied vessels sailed across the Channel to Dieppe on the French coast, carrying commandos and LCTs (Landing Craft Tanks) which were to execute eight assault landings, supported by from the air by bombers and fighters and the Navy's offshore batteries. The plan was to take the German held port for a short time, causing as much damage as possible to the enemy's coastal defences and facilities, whilst also gathering intelligence. Along with this it was hoped that the operation, also known as the Dieppe Raid, would boost morale both amongst the Allied forces and the French Resistance.
On the way across the Channel part of the convoy encountered five German ships and a battle ensued. This lead to not only the loss of men, landing craft and equipment, but also the loss of the element of surprise, although there have been arguments over whether the Germans already had intelligence about the operation. They were prepared and waiting by the time 5,000 Canadian troops landed near Dieppe. Many were mown down by machine guns before they even reached the shore. Of the tanks, only 15 made it to the seawall but couldn't get into the town. The rest sank in deep water or were became bogged down on the beach. The RAF did their best to cover the troops from the air, but the Spitfire and Hurricane squadrons were fighting far from base which reduced the amount of time they could fend off the Luftwaffe.
The losses were massive, with two thirds of the Canadian troops killed, wounded or taken prisoner, and the British lost around 800 men. Despite the failure of the raid to fulfil its objective valuable lessons were learned that contributed to the success of the Normandy landings two years later.