The Sinking of the Gwen ha Du

[davidwheeler]

In France there is a canal which linked Brest, an important naval base and port at the North west corner, to Nantes, on the River Loire. It is called the Canal de Nantes a Brest. Conceived in 1785, its purpose was to create an inland navigation  between these two important commercial centres, safe from the prying eyes - and the guns - of the British navy. But by the early 20th century, falling volumes of canal traffic, and an increasing need for electricity, caused the authorities to plan a dam at Guerledan, where the River Blavet, and the canal,  ran along the borders of Departments Cotes D'Armor and Morbihan. This hydro-electric dam, started in 1923 and finished in 1929 flooded the valley of the river and submerged it and the canal, and 16 of its locks. And a lot more besides. At its deepest part, close to the dam, to a depth of 50 metres. It blocked the through route of the canal. An understanding, at the time,  to create a system of locks to surmount the dam and thus reinstate the canal route came to nothing. It has not happened since. The cost, and the engineering challenge, would be considerable. 

When the dam was filled, a vast new inland lake was created, 55 million cubic metres of it, covering 300 hectares. The architect of the dam, Monsieur Auguste Leston, considered that he needed a boat to get about. To show off his creation to those officials come to wonder at it. Many did, from all over Europe.

So he bought an old lobster boat. This small wooden vessel of 8.45 tons, built in 1922 at Sables d'Olonne in the French Vendee, the 'Sans Gene', belonged to M. Georges Rouille and he fished lobsters in it with his younger brother and a deckhand. It was powered by a 12-14 cv Betus - Loire petrol engine. But in 1934, at the age of 41, M. Rouille decided to sell and M. Leston decided to buy. The 'Sans Gene' travelled up the Atlantic coast to Brest during the winter of 1934, entered the canal and passed along it into the lake. There its name was changed to 'Gwen ha Du', the name of the official Breton flag.

For the next five years it enjoyed a quiet life on the lake in the service of its master.

But in 1939, following the collapse of the French forces, the German army seized control of the dam. It requisitioned the 'Gwen ha Du'. Now it served its German masters. Now it was a military vessel, patrolling the lake, moving stores and equipment.

The hydro-electric plant at the dam, and its transformer station in nearby Mur de Bretagne were early priority targets for attack by the British, since the plant was the principal source of electricity for the German submarine base in Lorient. Destruction of the dam itself was considered but rejected because of the potentially disastrous consequences of a breach for the nearby and downstream city of Pontivy. 

So the aim was the destruction of the transformer station by bombing, and harassment of the dam and its infrastructure and control buildings by strafing attacks. Bombing by Boston 111A bombers, and strafing by Mosquito aircraft. But with attacks by Mosquitos on the transformer plant as well, as the occasion arose.

More of the story tomorrow.

[Heartland]

A serialised post this is rare, but to put it into perspective may be some mention should be made of canal craft sunk by axis bombing in World War 2 in the UK.

[davidwheeler]

Ai midday on 1st April 1943, a Mosquito F11, pilot P/O J.L.Mason, navigator P/O R.J.Roe, took off form RAF Colerne. Its mission: to attack the electricity generating buildings and equipment at Lake Guerledan, and the transformer station at Mur de Bretagne. Flying low over the coast and over the French mainland, it reached its target: 'approaching from the south, climb to 1500 feet, dive to 300 feet, long burst 20 mm canon at dam structures, impacts seen rooves and sides of central building; over dam, circled to south for second attack, long burst of canon fire, hits observed power structures and lines; on to transformer station at 1000 feet, dived to 300 for canon attack, guns jammed'. Turning back for another sweep of the dam, the pilot decided to abort, because smoke and flames, probably from pine trees set ablaze, effectively blanked out the dam buildings. So the Mosquito went back to Cornwall. The navigator noted that no enemy aircraft was seen, no ships, and no flak and thus no damage to aircraft or crew.

During this, or one of the Mosquito attacks, the 'Gwen ha Du' was hit by canon shell and sank to the bottom of the lake, 40 metres down.

But that was not the last to be seen of the 'Gwen ha Du'. 

Under the terms authorising the dam, the structure was to be inspected every ten years and this involved draining the lake. All 55 cubic metres of it. This was done in the years 1951, 1966, 1975, 1985 - and 2015. On each occasion the wreck of the 'Gwen ha Du' was revealed as the water receded, lying in the old bed of the  stream called Poulham, within sight of the dam. On each occasion a little more damaged. But in 2015 a lot of publicity was given to the event - 'The first time the lake is to be drained in 30 years'. 'A lunar landscape, not seen for thirty years.' ' Exploring the dry lake, an experience unlike any other'. A Visitor Guide was produced, with the 'Gwen ha Du' on the front cover. Thousands and thousands went to the site to look down at the line of the canal, the locks, numbers 120 to 136, the lock houses, the roads , the forests, the field boundaries, farm houses, villages, revealed for the first time in so many years, gradually as the waters drained away. With them came the trophy hunters and the vandals, ripping out planking and timbers from the wreck. Supporters of it sought to protect it until once again the lake began to fill and the 'Gwen ha Du' disappeared under the water.

This time for good. It is not proposed to empty the lake again. For inspection purposes, other arrangements have been made.

This is the story of the sinking of the Gwen ha Du, a very small victim of Allied fire power and the fearsome Mosquito, eighty years ago.