Canadians attempted to build a ship out of pykrete (a mixture of wood pulp and ice) during WWII. The wreck of this prototype is still at the bottom of Patricia Lake in Jasper.
Operation Tracer was a top-secret WWII mission in which six men were to be buried alive inside the Rock of Gibraltar so they could monitor enemy movements after the Rock’s capture. There was no way out and anyone who died within the chamber would have to be embalmed and cemented into the floor. The men understood that they would remain sealed within the facility for about a year, although it could be much longer. Provisions for a seven-year stay had been assembled in the complex. The entirety of the main chamber had been plastered and its floor covered in cork tiles, both methods to reduce sound transmission. The entrance passage had loose soil, to facilitate burials if needed.
10% of those conscripted in the UK in WWII were sent to serve not on the battlefield, but in the coal mines that powered the war machine. Some of these soldiers were not released from service until two years after the war ended. They were not formally recognized for their contribution until 1995.
Mitsuo Fuchida, the captain that lead the attack on Pearl Harbor, later became a Christian and settled in the US permanently.
Felice Benuzzi was a P.O.W. in Kenya during WWII. He recruited two others to stage an escape so that he could climb the second highest peak in Africa, knowing that there was no chance of a permanent escape. With scant food and only improvised equipment such as barbed wire crampons, no porters or guns, they traversed the jungle, encountering wild animals, and climb the mountain. Two of them reached a point ~5000 m high on the 5199 m mountain. And then they returned and broke back into the camp, as planned. He later wrote the book based on this, which was made into a fictionalized movie.
A Japanese Oil Tanker captain fell into a cactus at a Santa Barbara Oil Field, provoking laughter from the local workers. 5 years later he returned in an Imperial Japanese Navy sub and made the first mainland shelling of the US at that oil field.
The US considered dyeing Mt. Fuji black in WWII as psychological warfare against the Japanese.
Witold Pilecki, a Polish Army officer, volunteered to get imprisoned in Auschwitz to gather intelligence and escape.
Part of the reason why the Allied secret services could fool the Nazis many times is that the deputy head of the German Abwehr, Hans Oster, actively sabotaged the Nazi war effort.