Searchlight-homing bomb

[Dilandu]

Up until the late phase of World War 2, searchlights remains the main instrument for guiding anti-aircraft fire at night. Even with the appearance of radar systems they were initially used to aim searchlight beams, not directly control the guns - the precision needed for direct gun laying became available only around 1942.

On the other hands, electro-optical technology was quite advanced by the late 1930s, with the selenium photoelectric cells having widespread use.

So the idea: could the late 1930s technology be used to guide a small bomb along the searchlight beam, or lock on and track the searchlight itself? Such system could (theoretically) work as an optical analogue of early anti-radiation missiles - i.e. making searchlight crews nervous and forcing them to either risk being hit, or switching off the beam (and thus losing target). I.e. to serve more a deterrence weapon, by creating a probable danger for searchlight crews.

The most problematic part would probably be the narrowness of the searchlight beam. While beam obviously have enough intensity for the bomb seeker to easily track it (and the brightness would increase with bomb closing to the searchlight, thus improving accuracy), it is also quite narrow, and could move pretty fast. The solution may be for the bomb not to track exactly the beam, but use the beam only to lock on its source (i.e. searchlight itself), and then home on it from outside the beam path.

 

[Hood]

The RAE's 'Ben' naval SAM programme of 1943 was originally a searchlight beam-guided weapon so your idea is the reverse of that. Your main problem is getting a photo-electric cell sensitive enough to search for the narrow beam and them lock onto it.

 

[Dilandu]

The RAE's 'Ben' naval SAM programme of 1943 was originally a searchlight beam-guided weapon so your idea is the reverse of that. Your main problem is getting a photo-electric cell sensitive enough to search for the narrow beam and them lock onto it.

Well, if the carrier plane would drop the bomb as soon as it is lightened by the beam, then the search problem would be nullified; the beam is already here. And if I recall correctly, photoelectric cells of 1930s were more than sensitive enough to detect a bright light on darkened background.

 

[Tony Williams]

Up until the late phase of World War 2, searchlights remains the main instrument for guiding anti-aircraft fire at night. Even with the appearance of radar systems they were initially used to aim searchlight beams, not directly control the guns - the precision needed for direct gun laying became available only around 1942.

On the other hands, electro-optical technology was quite advanced by the late 1930s, with the selenium photoelectric cells having widespread use.

So the idea: could the late 1930s technology be used to guide a small bomb along the searchlight beam, or lock on and track the searchlight itself? Such system could (theoretically) work as an optical analogue of early anti-radiation missiles - i.e. making searchlight crews nervous and forcing them to either risk being hit, or switching off the beam (and thus losing target). I.e. to serve more a deterrence weapon, by creating a probable danger for searchlight crews.

The most problematic part would probably be the narrowness of the searchlight beam. While beam obviously have enough intensity for the bomb seeker to easily track it (and the brightness would increase with bomb closing to the searchlight, thus improving accuracy), it is also quite narrow, and could move pretty fast. The solution may be for the bomb not to track exactly the beam, but use the beam only to lock on its source (i.e. searchlight itself), and then home on it from outside the beam path.

Two obvious countermeasures:

1. add a remote control system to the searchlights, so that the crews are sited a safe distance away from the lights.

2. install decoy lights bright enough to lure the homing bombs, and only switch on the real lights later.

PS also attach hoods to the searchlights, so their light can only be seen over a very narrow angle.

 

[Dilandu]

1. add a remote control system to the searchlights, so that the crews are sited a safe distance away from the lights.

It would not exactly be very useful. If the crews are somewhere else, they would have real troubles with pointing searchlight at the plane due to the different line of sights. Unless they are very close (which would negate the whole idea), the parallax would kick into play.

2. install decoy lights bright enough to lure the homing bombs, and only switch on the real lights later.

A possibility, yes. But it would work only as long as bomber crews are unaware of such trick.

PS also attach hoods to the searchlights, so their light can only be seen over a very narrow angle.

This may be an actual counter-measure, yes.