[Johnny .45]

I'm curious about a few things regarding tracer ammunition in WWII planes.
1.) Did WWII planes use tracers? Was there a certain service that did, others didn't? You can see them in guncam videos at times, but I'm still unclear if they were used by all combatants, or all the time, or what. I know they didn't use them in night-fighters, to avoid damaging night vision and pinpointing the attacking fighters location. I'd always assumed that most planes used tracer ammo, but I just read something the other day about RAF BoB pilots...how "when the pilots saw tracers coming out of their guns they knew they were into the last 20 or so bullets"
That suggests to me that the rest of the ammo DIDN'T have tracers. Or that ALL of the last 20 rounds were tracers, but that seems like a dumb idea...if I'm down to my last rounds, they'd better be at LEAST API-T rounds, not just plain tracer ammo that would hardly scratch a plane.

2.) Did cannon shells have tracers, or just MG bullets? I've seen shell-type lists that include shells marked as tracers (HE-T, AP-T, HEI-T, API-T, etc.), but I've also heard that in some planes (the Zero was one, I think) that kept their MG's for the tracers, so they'd have an idea where the cannon shells were hitting. I know that the Hurricane Mk IID with 40mm Vickers guns kept a single .303 Browning in each wing, exactly for that purpose. But what about smaller types, like 20mm?

3.) For those types that did have tracers (I'm PRETTY sure that US fighters used tracer ammo, but not positive), what would a typical loadout be? I know that infantry MG's will use a mix, like 1 round in 5 is a tracer, or 1 round in 10. I'd always assumed that the RAF used tracer ammo in the .303-armed Spitfires, etc, but I just found out the other day that they actually didn't mix AP, Incendiary and ball ammo in the magazines, they just loaded one gun with AP, one with incediary, and two with ball ammo (or something like that). So, did they mix tracer ammo in with it? Or was there a single gun dedicated to tracers? Or did the original British incendiaries double as tracer rounds? I know that the early types ignited on firing, and I guess the burning chemical could make a tracer-like glow, but how about after they went to the kind that ignited on impact? It supposedly made a flash and report when it hit, but that's not quite as good as a tracer, I wouldn't think.

I'm sure there's other stuff I'm not thinking of, but I have to go now. I'm sure I'll remember while I'm in the store and it's too late! That's just one of the little details that has bugged me on and off for a while...in the movies you always see the planes shooting at each other with long tracer streams coming out of the guns, and I never knew whether that was really accurate, or just to give a better visual effect.
And if fixed-gun fighters didn't use/need tracers, then did flexible-mounted guns use them? That'd make it a lot easier to hit a Bf 109 making a pass on my B-17, if my .50cal had tracer ammo loaded. They didn't have gyro-sights, so it would make it very difficult to pull any kind of deflection without some reference to where the bullets are actually going.