I heard that the Navy (historically, at least--don't know about today) placed a greater value than the Air Force on engine redundancy. Hence why we have both the twin engine F-18 (Navy) and the single engine F-16 (Air Force), even though functionally there's a lot of overlap between the two.
Sure, but then you also have the F22, F117, B2, A10, SR71, U2, and a bunch more I can’t think of right now.
Some helicopters have a single engine. Most have 2. They are still unreliable death machines, and arguably 2 engines makes the problem a bit worse (more moving parts). They are (sometimes) more tolerant of a single engine out, of course. But transmissions are often the weak spot with helicopters.
Single vs Dual has many factors, not just reliability.
A single engine failure on a SR71 (if I remember correctly) resulted in a airframe loss and ejection at relatively low speeds, and one at full speed would likely result in a complete crew loss on top of it - and it has dual engines. Think catastrophic near instant destruction.
Sometimes you just need more power than a single engine (with current tech) can provide in the space you have available, for instance.
Sometimes, like an A10, you really do want something that can take a massive beating and keep going.
A B52 can lose 2 engines with no issues, and theoretically up to 4 and still be controllable (depending on the distribution of the lost engines). But that isn’t because it needs reliability, but because it’s got 8 engines because it was designed to carry a metric shit ton of explosives, and it only had 60’s era tech jet engines.
Modern jets usually use 2 (much more powerful) engines for similar or even larger payloads.
