Hybrid jet-propeller planes in real lift where a weird thing that existed in the 40s & 50s, no type of them ever saw combat use or even limited production. In modern day not even much research is done on them. But what could allow them to see significant military use? The level of technology is near future.
what could allow them to see significant military use?
If there was no material enabling the construction of pure, jet only engines, turbo-propellers would become the limit for airplane propulsion, and therefore make this the cutting edge of technology.
They would probably need to be improved from the early prototypes like the Republic XF-84H
The XF-84H was almost certainly the loudest aircraft ever built, earning the nickname "Thunderscreech" as well as the "Mighty Ear Banger". On the ground "run ups", the prototypes could reportedly be heard 25 miles (40 km) away. Unlike standard propellers that turn at subsonic speeds, the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards. The shock wave was actually powerful enough to knock a man down; an unfortunate crew chief who was inside a nearby C-47 was severely incapacitated during a 30-minute ground run. Coupled with the already considerable noise from the subsonic aspect of the propeller and the T40's dual turbine sections, the aircraft was notorious for inducing severe nausea and headaches among ground crews. In one report, a Republic engineer suffered a seizure after close range exposure to the shock waves emanating from a powered-up XF-84H.
Asymmetric Warfare anti stealth
Having just looked up the XF-84H the first thing that springs to mind is a cruise missile.
The JU87 Stuka had a siren mounted under the engine that gave it its infamous scream - adding a psychological effect to dive bombing.
Imagine a warship launching a cruise missile powered this way. Missiles are normally fired broadside, and the shock waves travel sideways from the direction of flight, which would initially be rocket powered in any case while the wings, props, air intakes and things unfolded, so the crew would be unaffected.
After that this thing would hurtle toward its target at as low an altitude as possible at well over 800kph making the most awful racket, clearly audible to anyone it passed right out to the horizon. It may even damage structures it passed over directly.
Everybody in the target area knows somebody just had a really bad day.
Provided the opponent was unable to shoot this kind of aircraft down it would be an appalling terror weapon, while being as tactically useful as any other remote/self guided precision weapon system.