On Wednesday, tree experts at the annual meeting of the European Geosciences Union showed why they failed to do so until late 1944 
 
 "The story was in the tree rings," said Claudia Hartl, a researcher at Johannes Gutenberg University in Mainz, Germany. The Germans, however, had a counter-plan: producing vast quantities of artificial fog, enough to hide the ship and surrounding area from aerial view. A 1944 picture shows smoke rising from the Tirpitz following an attack by allied bombers in a Norwegian fjord 
 
 Arboreal casualties 
 
 "The smoke drifted into the forests surrounding the fjord and damaged nearby pine and birch trees, leaving behind a distinctive and unusual 'fingerprint'," St. George told AFP. In pine trees, needles usually last from three to seven years because they're evergreens.
– A German dendrochronologist stumbled on something puzzling while gathering wood cores on the Norwegian coast in 2016: some trees were missing rings. "We got back to the lab and measured the tree rings, and saw that they were very narrow—in some cases nearly absent—for 1945," Claudia Hartl tells the AFP. A local scientist had a theory, she explained Wednesday at the annual meeting of the European Geosciences Union: that it had something to do with the Tirpitz. The 820-foot battleship was the largest in Hitler's navy, and the BBC reports it spent much of WWII anchored and hiding along Norway's coast, including in Kåfjord, where Hartl observed the tree-ring anomaly. But then Allied forces found it, and that's when the trees suffered, believes Hartl. The Nazi ship released chlorosulphuric acid as a sort of "chemical fog" to try to cloak it from aerial enemy forces, and Hartl now believes the acid caused damage to the trees' needles. "If trees don't have needles they can't photosynthesize and they can't produce biomass," she explains, noting recovery can be a multi-year process as pine trees can retain their needles for as long as seven years. And that jibes with what she found: In one case, a tree had no growth for nine years and took three decades to revert to "normal growth." Near where the ship was stationed all the trees she studied were affected, with more than 60% not growing at all in 1945. She found the impact on the rings diminished with distance, with trees about 2.5 miles away starting to be unaffected. As for the Tirpitz's ploy, it didn't work: It was ultimately sunk. (Using ink and urine, this man recorded Nazi horrors.)