Fog.

This is coolbert:

Here as described a serendipitous scientific discovery with a military dimension.

From Newser and the article by Kate Seamons and thanks to both.

"Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed in order to analyze atmospheric conditions during different periods in history."

"Nazis' Attempt to Cloak Its Ship Affected Norway's Trees"

"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'"

CHEMICAL FOG AS USED TO CONCEAL THE POSITION OF THE MOORED GERMAN BATTLESHIP TIRPITZ CAUSING UNINTENDED ENVIRONMENTAL DAMAGE!

"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."

Artwork courtesy of John Makin. Click on image to see an enlarged view. Tirpitz even when moored an operational threat to the Arctic convoy system, the transport of war munitions to the Soviet Union. Measures to conceal the Tirpitz from aerial attack to include the disruptive paint scheme of the ship, camouflage netting, smoke pots and "chemical fog" as it is referred to.

To what extent "chemical fog" MORE EFFECTIVE than smoke [as given off by a smoke pot] I cannot say.

Tirpitz throughout most of the Second World War EVEN WHEN MOORED AND NOT AT SEA deemed a significant threat for which extraordinary measures necessary. Efforts to sink or disable the Tirpitz the stuff of legend!

I have been told that within a fifty-mile strip of land in northern France running from the English channel to the Swiss border a compass the use of more or less negated by the presence of so much steel in the ground, artillery bombardments of a prodigious nature from the era of the Great War to blame!

Such as is what occurs during wartime merely from an environmental standpoint.

coolbert.