It is the 60th anniversary of the dambusters mission, one of the most daring raids during World War II, which owed its success to trials in one of Wales' most picturesque areas.
Tests were carried out in the Elan Valley
Warplane designer Barnes Wallis developed the bouncing bomb which destroyed and damaged some of Germany's main dams after using the Nant-Y-Gro dam in the Elan Valley, near Rhayader in Powys for initial trials.
The 35-feet high dam was used for the secret experiments by government officials who needed a testing site for the bombs.
The area which was already used as a firing range by the military was the perfect location because of its remoteness.
Two trials were carried out on the dam.
In May 1942, the first live explosive tests took place. Although they were spectacular they did not damage the Nant-Y-Gro dam and further work was needed.
The Elan Valley was crucial in the testing of the bouncing bomb
But just two-months later in July, a second experiment was carried out using a 500 lb anti-submarine bomb containing 279 lb of explosive.
It was suspended in the middle of the 180 foot long dam and detonated. The explosion blasted away a massive section of the central dam wall.
The success of the experiment at the Elan Valley meant that a programme of highly secret trials were carried out in other parts of Britain with the end result being the famous Dambusters mission in 1943.
Beyan Lawrence, a local historian from Rhayader, said that the Elan Valley was vital to the success of the mission.
"During both wars, the Elan Valley was used as a firing range and people were well used to the sound of explosives," he said.
Lancaster bombers were used in the Dambusters mission
"They wouldn't have been shocked by the noise of the second bomb test.
"People living here didn't know what was going on there because it was all secret.
"The Elan Valley was crucial in the testing of the bouncing bomb - it was used to check what amount of explosives to use and the distance," he added.
The bouncing bomb was designed to spin backwards at 500 rpm, skipping over torpedo nets, before detonating against dams in enemy territory.
Some 19 Lancaster bombers of 617 Squadron, each with a crew of seven men, took part in the raid to knock out German electricity and water supplies.
The low-level attack targeted the Mohne, Eder and Sorpe dams in the Ruhr, near Dortmund, which were vital to Germany's industrial production.
The raid was deemed a success as the destruction of the Mohne and Eder dams caused widespread flooding and disruption of rail, road and canal communications.
The attack was credited with boosting the beleaguered morale of troops and was made into the film The Dambusters starring Sir Michael Redgrave in 1954.
On the night of 16 / 17 May 1943, the Mohne and Eder dams were successfully breached but two other attacks on the Sorpe and Schwelme failed.
But the raids came at a cost: eight aircraft and 53 crew were lost during the night.