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The Nazis’ efforts to protect one of their biggest battleships from Allied attacks during World War II left a lasting mark on the Norwegian landscape.

Commissioned in 1941, the German battleship Tirpitz spent much of the war stationed in various fjords along the coast of Norway, in an effort to prevent an Allied invasion there. To keep the 820-foot vessel—which wartime leader Winston Churchill called “the beast“—from being seen by planes flying overhead, the Nazis surrounded it with a smokescreen of thick, artificial fog.

According to a new study, the chemical fog permanently damaged the surrounding trees, an impact that is clearly visible in the pattern of their growth rings. Claudia Hartl, a dendrochronologist from Germany’s Johannes Gutenberg University, was collecting wood cores in the coastal Norwegian village of Kåfjord when she noticed that the growth rings in some trees dating to around 1945 were either tiny, or completely missing, reports BBC News.

Alta fjord, Norway. (Credit: Getty Images)

Alta fjord, Norway. (Credit: Getty Images)

Dendrochronology, or the dating and study of growth rings in trees, allows scientists like Hartl to form a complete picture of the past climate of a region, as each tree ring reflects the weather conditions of the growth season in which it formed. Extreme cold or insect attack can stunt tree growth, but not to the extent that Hartl noticed around Kåfjord.

Then one of her colleagues suggested the missing tree rings could be related to the Nazi battleship. The Tirpitz had been anchored in Kåfjord in 1944 when it came under attack by Allied bombers. According to the new study, the Tirpitz then released a fog of chlorosulphuric acid to act as a smokescreen.

“We think this artificial smoke damaged the needles,” Hartl told the BBC. The damage prevented the needles from performing photosynthesis, which enables the tree to grow. Once an evergreen tree’s needles are damaged, it takes a long time for the tree to recover. In one of the trees Hartl and her colleagues examined, they saw no growth for full nine years after 1945. And even once it recovered, it took 30 more years for the tree to achieve its normal growth.

Smoke screens put up in attempts to hide the Tirpitz battleship drifting in the waters. (Credit: Imperial War Museum)

Smoke screens put up in attempts to hide the Tirpitz battleship drifting in the waters. (Credit: Imperial War Museum)

The Tirpitzsaw its first bombing attack by the British Royal Air Force (RAF) in January 1941, as it was still being completed on a dry dock in Wilhelmshaven, on the North Sea. Soon after its commission in the Kriegsmarine that year, it was sent to Norway, where it spent the next three years menacing Allied convoys headed for Russia. The giant ship’s presence along the Norwegian coast forced the Allies to keep a large fleet in northern waters to guard against its attacks, and the RAF and Royal Navy both made repeated attempts to sink it over those years.

In November 1944, the Allies finally tracked down the Tirpitz in Tromso fjord, located to the west of Kåfjord. Thirty RAF Lancaster bombers armed with 12,000-pound “Tallboy” bombs hit the German battleship and sank it after about 10 minutes, killing some 1,000 members of its crew and putting an end to Nazi naval warfare in northern waters.

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