Gunnar Sønsteby obituary

Most highly decorated hero of the Norwegian resistance in the second world war
Gunnar Sønsteby
Gunnar Sønsteby Photograph: Arnephoto/Wikipedia

The most highly decorated hero of the Norwegian resistance in the second world war, Gunnar Sønsteby, who has died aged 94, became a master of disguise, forgery and espionage to sustain a prolonged sabotage campaign against the Nazi occupiers of his country. He had taken the invasion personally, resenting "the humiliation of seeing those green-uniformed creatures tramping our streets," as he recalled in his memoirs.

The Germans were certain to seize neutral Norway once the "phoney war" ended in spring 1940. They were heavily dependent on Swedish iron ore, which went by rail to Norwegian Atlantic ports when the direct route through Sweden and across the Baltic was closed by ice. It was then shipped to Germany via the complex waterways between the mainland and offshore islands. Most of this route was inside Norwegian waters and therefore legally sacrosanct.

Meanwhile the SS Altmark, former supply vessel for the pocket battleship Admiral Graf Spee, scuttled after the battle of the River Plate in December 1939, sailed undetected from South America to the North Cape, where she entered Norwegian waters. British destroyers illegally forced her into a fjord south of Stavanger in mid-February. When they boarded, British sailors were amazed to find 299 British prisoners on board, from ships sunk by the Graf Spee – a handy excuse for breaching Norwegian neutrality.

In response, however, the Germans in early April invaded Norway, which fell in two months, regardless of stubborn local resistance and a generally inept Anglo-French intervention. Sønsteby resolved to get to Britain in a small boat to join a fledgling resistance unit, but frostbite in northern Sweden on his way to the coast forced him to return to Oslo.

He volunteered for the initially cautious Milorg (military organisation) resistance movement but, impatient for significant action against the occupiers, began to gather intelligence by brazenly offering his services to the pro-Nazi Norwegian state police, giving him excuses to travel and gather information. He was able to cross the long and often remote mountain border into neutral Sweden several times, making his way to the British embassy in Stockholm, where he contacted the Special Operations Executive (SOE), the agency set up to organise sabotage in occupied territories. He became SOE agent number 24.

One of his first assignments was to gather information about the new U-boat and port facilities the Germans were building at Trondheim, in the far north. When his colleague's radio transmitter broke down, Sønsteby crossed into Sweden again to obtain spare parts. To facilitate his travels within Norway he taught himself how to forge an array of German documents. His many disguises enabled him to evade the Gestapo.

In summer 1942 he stole banknote-printing plates of the Norwegian state bank to help the SOE fund operations in Norway, smuggling them over the Swedish border. One of his accomplices in this escapade was arrested by the Gestapo, prompting Sønsteby to lie low in Sweden. While there he was persuaded by SOE to go to Britain for special training.

Returning to the Oslo area by parachute in November 1943, he found the capital a much more threatening place than it had been. His father and a number of resistance colleagues had been imprisoned. Tension between Milorg and SOE had risen as a result of British pinprick commando raids on Norwegian targets, which prompted brutal Nazi retaliation.

Sønsteby now took a co-ordinating role covering the greater part of Norway, including the bulk of the country's long Atlantic coastline and the principal ports. As a captain, he commanded "Norwegian Independent Company 1", later known as the Linge Company in honour of its executed first leader. A long list of subsequent bold sabotage operations included some strategic coups, such as destroying official records the Germans were using to round up young Norwegians for the Russian front or forced labour. Arms plants and artillery batteries, chemical works and German aircraft were blown up and merchant ships sunk.

He organised the destruction of 75,000 ration books, which frustrated a German plan to reduce the already meagre official ration. When the allies invaded Normandy in June 1944, the Norwegian resistance sabotaged the railways, preventing the Wehrmacht from sending reinforcements southwards.

Sønsteby, born in Rjukan, south Norway, was a student in 1940. After the war he went to Harvard to complete his studies and worked in the oil industry abroad and at home. Uniquely he was awarded the War Cross with three swords, the highest decoration ever conferred by Norway, as well as the British DSO and the US Medal of Freedom. A grateful nation and royal family honoured his heroism throughout his long postwar life.

His wife, Anne-Karin, and three daughters survive him.

Gunnar Fridtjof Thurmann Sønsteby, Norwegian resistance fighter, born 11 January 1918; died 10 May 2012