Wartime means brainstorming new ideas for technology to defeat the enemy. Some ideas caught on; others didn't, and both types of innovations could appear rather silly in retrospect. But hey, if something looks stupid and works, then it isn't stupid. Like the tandem bike with no wheels the Germans used through two world wars.
During World War I, the German army outfitted its troops with "pedal-operated" generators, i.e. bicycles with a bigger dynamo instead of tires. On these tandem bicycles, two German soldiers would sit together intimately, pedaling for power and going nowhere -- like the least romantic French holiday ever. When stumbling upon these bicycle frames, British soldiers marveled at them like it was some weird alien tech. As one officer's letter read: "It is exactly like a tandem bicycle without its wheels. I am not sure if it ever was a bicycle." Leave it to the Germans to create military equipment that can also induce philosophical crises.
The bicycle was a generator that produced enough electricity to run radio communications, so therefore not as dumb as it looked. Other wartime technical experiments in this list were not so successful, like the flaming wheel of death known as the Great Panjandrum. See a video of the formerly classified Great Panjandrum tests and more in a list at Cracked.
(Image credit: Imperial War Museums © IWM (Q 79569))