Dambusters rehearsing at Abberton Reservoir © Gary Eason / Flight Artworks

Colchester, 17 November 2015

One of the delights of this part of the world is the number of nature reserves within a short distance of my office.

Among them is the Essex Wildlife Trust haven at Abberton Water, a reservoir – recently expanded – that is a specially protected, internationally important wetland because of its resident and transient wildfowl populations. 

In spring 1943, when the reservoir was only a few years old, it was visited by a flock of altogether more sinister 'birds': the specially adapted Avro Lancaster bombers of 617 Squadron – who in May that year would undertake an extraordinarily daring raid against dams deep in Germany and in so doing acquire their famous nickname, the Dambusters.

It is fairly common knowledge, thanks in no small part to the celebrated 1955 film about the operation, that the aircrews trained for it in the Derwent Valley in Derbyshire, at Howden and Derwent Dams.

Less well known is that they also tested their extremely low-level precision attack at Eyebrook Reservoir, near Uppingham on the Leicestershire-Rutland border – and here, at Abberton.

Topography

Remarkably, in their final rehearsals, Abberton was the stand-in for the Edersee. I remark on it because the landscape through which the Eder reservoir twists is picturesque, steep-sided wooded valleys. I have been there (in the pouring rain); it is pretty, green countryside as you can see from my photo.

The narrow, steep-sided valley below the Eder dam

The terrain at Abberton, on the other hand, is rather flat and largely featureless. To the casual observer the two locations could hardly be more different.

It has been suggested that they look similar from the air. Well, no they don't – and in any case, the Lancasters of 617 Squadron were not exactly going to be approaching "from the air", they were tree hopping.

It seems more likely that it provided a useful navigation exercise: Abberton is about the same bearing from the Eyebrook as the Eder is from the primary target that night at the Möhne – albeit nearly twice as far.

Even weirder, you might think: the Derwent Dam with its distinctive towers was the stand-in for the Sorpe, which has a totally different construction and no towers, and was hit along its length rather than at right angles – by the Upkeep dropped by bomb-aimer George Johnson, now the last British survivor from those who took part. 

Full dress rehearsal?

The squadron's official historian, Dr Robert Owen, told me: "Somewhere in the Lake District, such as Ullswater, would have been a better representation if a realistic rehearsal for the attack on the Eder were intended.  

"This perhaps reinforces the view that Abberton was used rather because it was a large stretch of water at a location that was conveniently placed in relation to the cross country routes, rather than for its physical characteristics of the target."

At any rate the squadron's leader, Wing Commander Guy Gibson, recorded in his flying log book that a "full dress rehearsal" was carried out at "Uppingham Lake and Colchester Res."  (his terms for the Eyebrook and Abberton) on the night of 14 May 1943, two days before Operation Chastise itself. He added: "Completely successfull [sic]".

Now, I have been involved with a fair bit of theatre over the years, and the point of a "full dress rehearsal" is to run the whole show as if it were the real thing.

What is the single most defining characteristic of the dams attack? Surely the extraordinary sight of those huge, revolving, 4.6-ton cylindrical depth charges bouncing across the water after being released at a precise speed, height above the surface and distance from the target.

Steep climb-out

Of course in a rehearsal they were not actually going to let off these massive weapons – the only live test of one had taken place many miles off the Kent coast. But the description "full dress rehearsal" does suggest they did spin up inert ones and sling them across the water to test all other elements of what was to unfold – no? 

"The aircraft did not drop any weapon, and it is unlikely that they even carried an inert Upkeep on these runs," Dr Owen said.

"The aircraft ran in across the lake, using their spotlights to achieve the correct height, fired a red Very light [pistol flare] as they crossed the dam, then climbed steeply away (possibly to simulate the manoeuvre required for the exit from an attack on the Eder dam)," he said.

This steep exit was necessary because the bluff beyond the dam rises to almost 1,400ft (425m) within about half a mile, the river valley turning sharp right.

You might recall that the 1955 film The Dam Busters does show 617's Lancasters dropping small practice bombs near a floating target buoy at the Derwent. Never happened, apparently, not on any British reservoir. This aspect of the training was done on the Wainfleet range on the Lincolnshire coast.

Which brings me back to my picture, depicting the special Type 464 (Provisioning) Lancasters running across the water at 60ft as determined by their spotlight altimeters — but not carrying any weapons.

What prompted me to double check all the details was that a big framed print of this is going to be hanging in the Layer Fox pub near Abberton reservoir, and I promised to write an extended caption to accompany it. Look out for it if you're having a pint.

Cheers!

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