There were a number of different raids that were aimed at the Norsk Hydro (company name) Vemork plant in Rjukan, Norway. These included three commando attacks and a bombing raid. The point of these raids was to prevent the Germans from making "heavy water," which was a step towards production of a nuclear weapon.
The first commando raid was called Operation Freshman. In this raid, British paratroopers were supposed to meet up with Norwegian agents who had been parachuted in to the wilderness near the plant months before (in Operation Grouse). It failed because the airplanes carrying the British crashed in bad weather.
The second commando raid was called Operation Gunnerside. This was a land attack by saboteurs. Gunnerside was quite successful and ended up destroying the facility.
However, the facility was rebuilt, which is when the bombing raid was attempted. This raid did not do much damage to the facility but did convince the Germans to move the facility to Germany. As they were doing so, the third commando attack occurred. This one sank a ferry carrying the facility and the heavy water that had been made to Germany.