Tracers.

[Delirium]

Look at all the WWII gun cam footage you can find and so far as I have seen they all have one thing in common, they all used tracers.  The pilots used the tracers to adjust their aimming point.

Not all of them used tracers and I can recall a few gun cams where tracers were not present, only smoke trails.

[Traveler]

Not all of them used tracers and I can recall a few gun cams where tracers were not present, only smoke trails.

My Dad flew P47's and P51's in WWII according to him, they always used tracer ammo, the only thing that changed was the number of tracer rounds to ball rounds.  And not every gun had tracer ammo in the belt  only the two inboard guns on the P47, not sure about he P51, but not all 6 guns had the tracer ammo in the belt.  So perhaps you saw gun cam film taken at the end of a flight or fight and the tracer ammo was exhusted at that point. 

[BnZs]

My Dad flew P47's and P51's in WWII according to him, they always used tracer ammo, the only thing that changed was the number of tracer rounds to ball rounds.  And not every gun had tracer ammo in the belt  only the two inboard guns on the P47, not sure about he P51, but not all 6 guns had the tracer ammo in the belt.  So perhaps you saw gun cam film taken at the end of a flight or fight and the tracer ammo was exhusted at that point. 

Your Dad's experience does not cover the entirety of WWII

"[The commanding officer] ordered the tracer ammo removed...I'll never forget the spectacular results we got. Our kill rate went up from 50 to 100 percent."

--Colonel Charles W. King, USAAF
5 victories, WWII, as quoted in Fighter Combat by Robert Shaw

I've read a German aerial gunnery manual that speaks of some pilots removing the tracer rounds from their ammo belts as well. So apparently it was done on both sides.

[Delirium]

My Dad flew P47's and P51's in WWII according to him, they always used tracer ammo, the only thing that changed was the number of tracer rounds to ball rounds.   

As BnZ said.

 I respect his service but his view of the war was a keyhole view; absolutely facinating one that most of us would give much to experience first hand from the safety of our computer chairs, but a limited view none the less.

Tracer ammo wasn't always used.

[MORAY37]

On.

Tried both ways and find the surprise factor with them off is minimal.  Either the red guy has SA or doesn't.  Since I don't pull the trigger in fighter vs fighter engagements at anything more than D-200, having them off doesn't mean jack.  I'm already close enough to read his clipboard, and 200 yards was roughly the historical norm for pulling the trigger.

I find that tracers allow me to correct on crazy angle approaches to BUFFS, where I start shooting at D-800 or so.  High/low 1:30 seems to be an especially interesting lead for me personally, and I need to walk them in a bit.  Standard 3:00/ 9:00 approaches need just a bit of calculation with tracers, as well.