A term I’ve seen used in a few of the aeronautical books my grandfather gave me as a kid and applied to planes such as the F-106 Delta Dart.
I was never too sure though of it’s significance. Did it come from a time when only the more advanced aircraft had the equipment necessary to fly at speed without the pilot being able to see the ground or horizon?
More to do with equipment to see and shoot the enemy without actual visual contact IIRC. Also the capacity to depart and return in bad weather. Surprisingly or not, a lot of fancy foul weather navigation gear was left out of many fighters in the era for the F-100 series aircraft. Things were not nearly so sophisticated, computerized nor light in weight as it is today…
Which leads me onto another question I was tempted to ask, would severe weather have such a negative effect on jet engines that it might extinguish them? Could a jet engine suck in so much water from precipitation that it would stop working?
Thats a damn good question, in a nutshell they can actually tolerate rain just fine but ice can be an issue. Article covers it nicely.
I remember a DC-9 that crashed after it flew through a hail storm.
In addition to what GusNSpot said, there are still fighters being operated today (notoriously, most variants on the MIG-21 and -23 series) which are NOT “all-weather” due to radar or other technical limitations on combat during low-visibility conditions.
You’ll often hear the term “day fighter” thrown about in a similar context, referring to aircraft with no provisions for engaging targets at night. This term is most common in the light air-to-ground role and referring specifically to aircraft with an inability to positively ID and engage ground targets in darkness.