This has nothing to do with the X-Men character of the same name. Operation Jubilee is the codename for a raid that occurred on the coast of France on August 19th, 1942. It was the largest seaborne raid of World War II that wasn't intended to make a lodgement, and also failed spectacularly. In Canada, this operation is synonymous with waste and failure. It's better known as:
The Dieppe Raid
This mission was a clusterfuck from the beginning. Basically, the idea was to use a major raid to capture a French seaport from the Germans to see what the reaction time of German High Command would be; in addition, the Allies wanted to see what the reaction of the Germans would be to a raid in force, and hopefully draw the Luftwaffe into a battle where the RAF would apply overwhelming force and cripple the defenders of German-held France.
None of this worked. First of all, the mission was originally set up to go in July, but the Germans figured the damn thing out, and hit the buildup with bombers. So, the Germans had a pretty good idea something was coming. Secondly, Mountbatten (the guy in charge of the raid) didn't really have much permission to launch the attack, so his intelligence was out of date. Thirdly, the forces brought were wholly insufficient to pierce Hitler's Atlantic Wall.
Let's talk about the Atlantic Wall for a moment. This was one of Adolf Hitler's little projects wherein he thought the Atlantic Coast of the Reich should have an impenetrable wall build up upon it. It wasn't a reality, but most French ports were already fortified, and so Hitler added a bit to them, specifically in the form of German soldiers. The Allies targeted Dieppe because, quite frankly so they could blow stuff up as they withdrew. They were to find out that hard targets were a poor choice for an amphibious assualt.
Finally, the plan needed soldiers. Canadians were chosen, for no better reason than they hadn't been in a fight in too long. Add in some commandos to take the flank, a few tanks, and no direct fire naval support, and you have a huge recipe for disaster and damnation.
As you can see, Dieppe is surrounded by fucking cliffs. Brilliant, isn't it? Fucking cliffs! Rule 1 in amphibious warfare: DON'T ATTACK FUCKING CLIFFS.
Rule 2 in amphibious warfare: have direct fire support from the fucking navy! It's not like Canada was bobbing around in rowboats, anyway. They were being brought along by the Royal Navy. They had ships. They just didn't care to use them.
Rule 3: air support is a good thing. The RAF sent in like 70 squadrons, most of which were Spitfires operating at their maximum range, and completely outclassed by the Fw-190s they came up against. With little time to linger, they had to bug out or be shot down after a very short engagement. Longer range fighters would be needed in order to support future raids.
Rule 4: DON'T ATTACK CLIFFS.
So, the attack went down, and was a total clusterfuck. The commandos did their job pretty well, but the Germans in the centre, where the Canadians were attacking, held and inflicted around a thousand fatalities on the day. The landings were delayed, letting the Germans take all the time in ze veld to get ready for the attack. Adding on to that, the Allies had no idea what the beach conditions were like - no tanks got off the beach past an anti-tank barrier.
It would have been nice to blast open the anti-tank barrier, with say, naval support, but six destroyers just didn't have the short-support capacity needed to effectively blow shit up for the landing. In the end, the boys barely got off the beach, and the Canadians took something like 60% casualties in the raid.
Dieppe changed the way the Allies looked at amphibious assault. It became obvious that you couldn't do this on the cheap, that you needed to plan and plan and plan. Future assaults would have prodigious aircraft cover and direct fire support; save for the Torch landings in November, there would be no more attacks on harbours. There would be airborne and better tank support. Armoured vehicles designed to clear beach obstacles were designed.
Still, though, 907 Canadians died on the beaches of Dieppe, a cost far too high to pay for lessons that should have been well-known already. A damn tragedy.