Necessity, as the saying goes, is a Mother. War creates new necessities and therefore prompts the acceleration of technology. However, the examples you provided show how certain historical fallacies persist about war and technology.

Jet engines
- Frank Whittle was working on his jet engine designs for years before the outbreak of WWII. He actually patented his concepts in 1930 and founded Power Jets Ltd. in 1936. However, he was operating on a shoestring budget and progress was kind of slow. His first prototype was tested in 1937 but the first plane powered by one of his engines didn't fly until 1941. This made it the fourth nation to fly a jet, following the German He-178 in 1939 using an engine developed independently by Dr Hans von Ohain and Campini-Caproni CC-2 hybrid in 1940. The first jet was the Coananda-1910 flown briefly in 1910(!) before being destroyed in a crash.

Radar Work on radar began before the war, spurred in large part by the growing threat from Nazi Germany. The British had an operational radar system in place before WWII began in Europe and it was instrumental in winning the Battle of Britian. The Germans had independently developed their own radar systems as had the Americans. The British system was the most comprehensive at the start of the war, while in some respects the Germans were more advanced technologically. We had a primitive radar system operational in Hawaii before Dec 7, 1941 but it's warnings of a large number of inbound aircraft were not taken seriously. The war did spur tremendous technological development in radar but not the invention of radar itself. I strongly recommend the book, "The Invention that Changed The World" for this topic.

Liquid Fueled Rockets This is another example of a technology first invented in peacetime (Goddard in 1928) that advanced slowly but steadily in the years leading up to the war. WWII caused a lot of money to be pumped into rocket development, especially German money, and tremendous progress was made. However, the technology really didn't play any decisive role in the war and the money could probably have been better spent on producing practical weapons than on building long range rockets.

Antibiotics This is one area where the war had a huge impact on our lives to this day. At the start of the war, the closest thing to an antibiotic were sulfa drugs. They were useful but not what was needed to treat huge numbers of battlefield injuries, frequently involving nasty things like dirt blown into wounds by explosives. The British picked up Flemming's 1928 work and through a lot of effort found ways to produce penecillin in mass quantities. This has saved millions of lives around the world, probably more lives than were lost in the war (an estimated 100 million).

Digital Computers There were computers before WWII. For example, in 1937, Dr. George R. Stibitz pioneered the use of electical relays for digital computing at Bell Labs. Others expanded the idea to use vacuum tubes for faster processing. Of course, Collosis and ENIAC were wartime outgrowths of this research, but the seeds were laid before the war.