I rather suspect that, given the description of the missiles, that they are being launched from more than a kilometre away. A kilometre is far enough that escorts are sort-of leaving their bombers exposed, but it is plenty close enough to spot and intercept incoming craft. Not reliably maybe, but the description leads me to believe that they are launching missiles from far enough away that initial interception just isn't plausible. A fighter can get into 300 metres if it wants to, especially if it is using cannons. Yes, the missiles are huge, but they are not that huge. 300 metres in open-air is insane for explosives. Yes, they might hit once in a blue moon, but practically, the blast just won't stretch that far. A sphere with a radius of 300 metres has, umm, 113,097,335m3 volume? And it has, maybe, assuming a complete lack of sanity, 200 kilograms of explosive to fill that space? No, wait, it actually said... the old missile was 50 pounds and the new one is 25. Which is something puny in metric... let's say 25 kg... the density of air is... Oh, let's say 1m3=kg. Yes, certainly, the initial blast is is doing its own thing, but 6 orders of magnitude? Then there is stray bits of missile that might somehow be travelling in the direction of a plane occupies... a proportion of its view that I am really not interested in calculating, but a 20 metre long plane at 300 metres is not large compared to the area that is not plane... and a projectile would have lost a very great amount of velocity over that distance, and it wasn't exactly a bullet to begin with, and there are bullets that aren't much good after 300 metres... If it works as advertised and blows up triggers at 300 metres, then it should be plenty to protect our planes and plenty for escorts to blow up enemy planes if they get the things close. And a timed arming trigger is not a difficult revision. On the other hand, maybe they are armed in transit for some reason, like they never bothered to do basic safety checks or they somehow managed to have a homing missile that doesn't have a complex enough trigger to include an arming signal, in which case they go boom as soon as our fighters get close... Likely, the enemy planes, if there is one of our heavier interceptors equipped with one of these things(and I recommend we include some with our formations, it would have to be worth a couple of cannons on at least a third of our thunder whatevers and most of our Haasts.) in range, will explode as soon as they hit the missile button, which is going to spray enemy plane all over the place. Not "300 metres" all over the place, but enough that our fighters may not want to spend too long dogfighting anything with missiles. Of course, anything with missiles ought to steer like a cow, so dogfighting shouldn't take long...