Passive air defense questions

At night they can use fake fires, flares, and fake terrain features to misguide bombers; both the British and Germans used them to good effect. The US actually had painted terrain features on major factory roofs to make it look like a field or something.

https://en.wikipedia.org/wiki/Military_deception

Deception played an important part in the war in North Africa. Steven Sykes built a dummy railhead to protect the real railhead at Misheifa for Operation Crusader.[29] Geoffrey Barkas led Operation Sentinel and Operation Bertram which succeeded in deceiving Rommel about allied strength and intentions before the decisive Second Battle of El Alamein.[30]

Decoy targets, decoy factories and false fires, misdirection.

Neil Armstrong did have the wing on his Panther damaged by a wire strung across a river valley by the bridge he was bombing.

Taking a wider view, false intelligence e.g. V1 results via XX Committee.

To keep the enemy from finding you: camouflage nets, camouflage paint (Difficult to do with an airfield or harbor but may be suitable for a few key buildings such as control towers or hangars) Smoke screens, artificial mist, decoy targets...

Against enemy night bombers: Strict enforcement of darkening rules on the target and some decoy fires a few miles further down...

To keep the enemy from getting close enough for a direct hit: Barrage balloons, barrage kites, barrage cables where the terrain allows for it. Not quite satisfactory against high flying carpet bombers but might deter some strafing or low level bombing.

To keep enemy bombs from doing too much damage: Move as much infrastructure as possible inside bunkers or underground or in otherwise hard to reach terrain. The prime example of this would be the German u-boat bunkers in Saint Nazaire, but the American Minuteman rocket bunkers or the Swiss airfield hangars hewn into the mountainside are good illustrations too

Rivers and lakes make good navigation marks, so some were hidden by camoflage, floating coal dust on the water was one such method (used on lakes and resevoirs mainly).
The Whole ARP, system developed by the British in the 1930's has been termed as passive defence measures against air attack, I would concur with that conclusion. If your enemy know that you are prepared for the consequeces of an attack then they might be less enclined to attack in the first place.
I would also put the shadow factory scheme into this classification as a passive defense measure.

Would the various countermeasures to the German Knickebein system (see the Battle of the Beams) count as passive defense. They mainly worked by confusing the German navigators so that they dropped their bombs in the wrong location. They were so effective that one bomber landed at an RAF base thinking they were back in Germany.

Cheers,
Nigel

Have a bunch of these across the border.
Watch as enemy waste thousands of pounds of explosives on fake tanks.
Buy yourself more of these tanks with the extra money.
Repeat.

Just Leo said:

Decoy targets, decoy factories and false fires, misdirection.

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A lot of misdirection was used during the major Soviet air raids of Helsinki in February 1944, where over 2,100 bombers of the Soviet ADD dropped over 16,000 bombs in three separate raids in and around the Finnish capital. The city was darkened, all public traffic stopped and radio transmissions ended. A large number of bonfires was lit up in Vuosaari to the east of the central parts of the city to give an impression that Helsinki in its entirety was more to the east than it actually was. The searchlights in the western parts of the city were deliberately not used and in Vuosaari designated AA batteries kept up a constant barrage to make it seem that also the majority of the city's active AA defences were located more east.

The later studies have estimated that these measures were quite effective and as a consequence, along with successful active defence (very effective AA fire, etc) and very good advance information from radio intelligence as to the timing of the attacks, Helsinki survived with a lot less destruction that might have otherwise been - after all, in terms of scale (say, the number of aircraft used) the raids were almost comparable to the Dresden bombings and they were specifically designed by the Soviets as a devastating blow, a show of force to make Finland drop out of the war. It has been said that the Soviet leaders who visited Helsinki immediately after the war were very surprised at how little damage the city had suffered.

I once saw a Vietnam war era picture of an airbase in Thailand where every slab section of concrete was a different (earthy) colour, ranging from dark brown through light brown to light grey to dark grey. Its just a matter of putting some colour into the concrete mix, but it broke up the outline of the airfield really well and made the planes parked on the hardstand harder to see.

A bit outside your timeframe, but one of the nasty tricks that can be played against low level penetration is adding a mortar to a light anti-aircraft unit. Load mortar with chaff, fire off when an aircraft is getting close. The TFR gets a massive return straight ahead, interprets it as a cliff, aircraft pulls up hard, gaining altitude and losing speed. Your battery of light cannon then opens fire into the now obvious, vulnerable target.

Also, radar reflectors. Easily made with two-by-fours and aluminium foil, yet the electronic-age counterpart to bonfires in fields to decoy visual bombing.

zeppelinair said:

Have a bunch of these across the border.
Watch as enemy waste thousands of pounds of explosives on fake tanks.
Buy yourself more of these tanks with the extra money.
Repeat.

Click to expand...

Reminds me of the first Gulf War of 1991, where the allies were flying up and down Irak trying to shoot down every Scud missile launcher they could find, lest one of them manages to fire a rocket into Saudi-Arabia or Israel. Afterwards it turned out the Iraqis were quite good at building inflatable fake launchers. They even found a way to position the air blower for the dummy launcher in such a way that it gave the decoy the right heat signature....

so yes... That is one more passive air defense: Give the enemy a more interesting target. Fake missile launchers might work, but real ones aren't that bad either. Just look at all the bombers the Allies spent in WWII destroying the German V1 launch pads in France. Bombers that weren't available to bomb the German industry in Germany that night.