The big weapon that comes to mind is the B-36 bomber.
The US fully expected that Britain would collapse and bomb Europe from America.The B-36 was the world’s largest bomber and one of the most complex. He also had to protect himself. For a while it was planned to have a small number of fighter planes in their belly, called “Gremlins”. They should fight the enemy and somehow get back into the belly of the plane. This idea was never realized.
The B-36 later became a strategic bomber, and Jimmy Stewart later played a pilot in a film about it.In real life, the plane was a massive investment ruin.
There were many, many weapons platforms that the Germans never used, especially in the field of rocket artillery.
The German plan was to replace conventional artillery with multi-stage missiles to increase distance and payload. Although they used some early models – the accuracy was too low. The “Rhine Messenger” rocket had an advanced design and fired at the unfortunate Amsterdam.
One of the better German designs that never bore fruit was the M213 revolver gun.
This design was the predecessor of many weapons still in use today, such as the DEFA and others, and stood ten years before the minigun with the same firepower. This weapon shoots 20 mm ammunition at 1700 rounds per minute. Had it been successfully put into operation, it could easily have eliminated any Allied bomber in a single pass. Of course, due to the use of ammunition and the weight, there would have been only a limited duration of use.
The Germans were also on the rise of all types of helicopter development, but these were never realized.
The Germans recognized the possibility of a helicopter, but the factory was bombed.
The Germans were on the rise of advanced infrared technology for night combat with tanks called “Vampire” – but it was very cumbersome to use.
The British were about to deliver the Gloster Meteor, a jet fighter.