Recognition Lights and WWII IFF

Matt Gunsch · **Posted:** Thu Aug 14, 2008 12:33 pm

how it was used was easy, just like a password. a different color and flash sequence could be used every week or how often they changed it. the pilot would then flash the ID lights in the days code, if he got it right, he landed, if he didn't, he might be landing via parachute.

Randy Haskin · **Posted:** Thu Aug 14, 2008 1:19 pm

Taigh Ramey wrote:

So the Tweet has a red passing light in the left wing?

Single light in the nose, opposite the landing light.

Randy Haskin · **Posted:** Thu Aug 14, 2008 1:24 pm

Matt Gunsch wrote:

how it was used was easy, just like a password. a different color and flash sequence could be used every week or how often they changed it. the pilot would then flash the ID lights in the days code, if he got it right, he landed, if he didn't, he might be landing via parachute.

Interesting description, but I'm trying desperately to understand how -- with lights flush mounted to the bottom of the wing and facing directly downward -- that would work.

Perhaps if you were manning a AAA battery and were looking at the airplane through binoculars, that's a viable idea. But, from inside another aircraft I don't see that working.

How would a pilot be notified that he was being "interrogated" and know to flash the appropriate sequence back? With the lights of the OTHER aircraft on the bottom of HIS wing, I just don't see how that is possibly how it worked.

Ken · **Posted:** Thu Aug 14, 2008 3:29 pm

I expected someone would have said that the lights were steady "on" (during approach to an airfield for instance). Today's code is amber only, tomorrow's code is red and amber together, whatever. But you're right, those are small lights and they're set at an angle best viewed from the ground. Sounds like a real stretch for an effective recognition tool.

Taigh Ramey · **Posted:** Thu Aug 14, 2008 4:28 pm

My impression is that they were used for ground to air recognition by using the code of the day. Remember the whole country was waiting for an air attack and there were ground observers everywhere. Maybe the interrogation was received via radio or other light signal when an aircraft arrived over a check point or when entering the pattern. I was surprised to read in the information posted below that the lower lights were used for air to air recognition too.

Maybe they had a similar use in the theatre.

The AN drawing has an approval date of 17 June 1942 and was inactive after November 1956 and then it was cancelled after March of 1959.

JDK · **Posted:** Thu Aug 14, 2008 6:48 pm

Interesting thread.

Ken wrote:

I expected someone would have said that the lights were steady "on" (during approach to an airfield for instance). Today's code is amber only, tomorrow's code is red and amber together, whatever. But you're right, those are small lights and they're set at an angle best viewed from the ground. Sounds like a real stretch for an effective recognition tool.

I dunno if this would perhaps show one way this kind of system worked in the 1930s. These are from some RAAF pilot's notes for the Hawker Demon and were given to me by a 90+ year old ex-Demon pilot. I know it was simpler days, but the idea of this kind of night flying seems terrifying!

Quote:

19. Night Flying.

A. On Tarmac.
Before the engine is started the navigation lights should
be placed ''ON”.

B, While Taxying.
(1) Having waved the airmen away from your wing tips and
receiving the "All Clear," continually clear the nose by taxy-
ing first to the left iand then to the right of your track as
you proceed towards the taxying post.

(2) When taxying up to an object, do not aim the aircraft
directly towards the object, but aim definitely to one side or
the other as speed and distance is difficult to judge in the
dark.

C. At Taxying Post.

1. Carry out cockpit drill making all adjustments for taking
off.

2. Signal aircraft letter on upward and downward identification
lights to request permission to take off, and on receiving
the letter back from the Aerodrome Control Pilot in green, turn
the identification lights on by -lushing switches down. If the
letter is received back in RED acknowledge with the letter "T”
and await.

D. At Leeward Flare.
1. With the leeward flare about 10 yards on your left, line
up the aircraft parallel with the flarepath.

2. Stralghten up the tail wheel by rolling forwards a few
yards.

3. Set Magnetic compass red on red.

4. Take off.

19. Night xxxxx xxxxxxxxx.
1. Carry out normal cockpit drill.
i.e. Throttle back to -1 or –1 1/2 Ibs boost.

b. trim aircraft for climb if necessary.
c check instrument readings.

2. Carry on climbing into wind to 1,000 feet.

F. During downwind leg request -permission to land by signalling
the aircraft letter on the recognition lights. On receiving
the letter back from the A.C.P. in green, put both, recognition
lights on by turning the switches downwards and proceed with
approach and landing. If the aircraft letter comes back in
RED -acknowledge with the letter ''T" and carry out another
Circuit.

G. After landing.

1. Taxy off the flare path with as little loss of time as
possible and taxy towards post keeping well out from
the flare path.

2. Set upward and downward identification lights to morse
by turning the switches “UP”.

3. Come to a standstill at the taxying post and carry out
cockpit drill, making all adjustments for take off again.

4. Signal for permission-to take off.

Hawker Demon (RAAF Museum archive)

Randy Haskin · **Posted:** Thu Aug 14, 2008 11:25 pm

James, that makes a lot of sense. Thanks.

Taigh Ramey · **Posted:** Fri Aug 15, 2008 9:54 am

I too would like to thank you James. That is the first reference I have read about the use of recognition lights.

While looking for more information on the lights in a B-24 manual I found that early and later aircraft had different systems. The early one seems to have had a two light system which sounds similar to the one in the Demon.

The book also mentioned that the passing light was to be used on airways.

Thanks again James,

Taigh

Matt Gunsch · **Posted:** Fri Aug 15, 2008 11:11 am

Randy and Taigh, there is one problem with what JDK posted and that is it is for a British aeorplane, not a US airplane. We all know they talk and spell funny over there and have strange names for the parts of thier aeroplanes.
From the P-38 pilots manual:
Three recognition light, red, green, and amber, are located in the underside of the gondola. On some airplanes a white recognition light is behind the pilot's compartment on the radio equipment. There lights are used as an aid in night formation flying, for signals, and, in combat, for identification.
The four recognition lights are controlled by switches on a control box on the right side of the cockpit. The control box in labeled LITE, the switches has 3 posistions: OFF, STEADY, and KEY. To turn the lights on, place the switches in the STEADY posistion. When the switches are placed in the KEY posistion, you must press the button on the top of the control box to turn the lights on. Use the KEY posistion for code or flash signaling.

Randy Haskin · **Posted:** Fri Aug 15, 2008 11:15 am

Matt Gunsch wrote:

Randy and Taigh, there is one problem with what JDK posted and that is it is for a British aeorplane, not a US airplane. We all know they talk and spell funny over there and have strange names for the parts of thier aeroplanes.

Well, clearly the passing wasn't done on the right!

Taigh Ramey · **Posted:** Fri Aug 15, 2008 12:24 pm

That's a good one Randy. Say, do the modern day Lend Lease F-16's in the RAF have control sticks on the opposite side of the cockpit?

JDK · **Posted:** Fri Aug 15, 2008 7:21 pm

Thanks, chaps, glad it was of interest.

Matt Gunsch wrote:

Randy and Taigh, there is one problem with what JDK posted and that is it is for a British aeorplane, not a US airplane. We all know they talk and spell funny over there and have strange names for the parts of thier aeroplanes.

Hmmm - British Commonwealth aeroplane, please!

I appreciated it was somewhat tangential, but it is a rare thing - a contemporary 1930s document of actual practice, not a modern interpretation of what they did then.

Apart from the operational reality and safety being rudimentary at best, the objective was clearly just getting up and down again (safely being a nice extra) - what the point was (night interception? bombing?) remaining unaddressed.

There's a number of 'differences' to be borne in mind here, apart from spelling and the rule of the road; 1930s aviation developed from 'seat of the pants' to fundamental airways and night (not 'all weather') flying in the 1930s. I suspect that US, British Empire and continental practice all developed more or less independently; and 1930-1941 and 1941-45 were two different eras in terms of night flight.

In the '30 there was unwarranted optimism as to the utility of some types at night, the Spitfire Mk.I being expected to act as a day and night fighter, and thus being equipped with lights and signalling devices to allow that. It was far from ideal in the role. I suspect US types like the P-39 and P-40 had just as unrealistic expectations placed on them. It was only in 1940-41 when the RAF Bomber Command and Luftwaffe both switched to night missions that the systems started to be refined and more realistic for both bombers and their predators - although the P-61 was a case of overkill based on 1940 RAF data.

Cheers,

Matt Gunsch · **Posted:** Fri Aug 15, 2008 9:33 pm

JDK wrote:

Thanks, chaps, glad it was of interest.

Matt Gunsch wrote:

Randy and Taigh, there is one problem with what JDK posted and that is it is for a British aeorplane, not a US airplane. We all know they talk and spell funny over there and have strange names for the parts of thier aeroplanes.

Hmmm - British Commonwealth aeroplane, please!

I appreciated it was somewhat tangential, but it is a rare thing - a contemporary 1930s document of actual practice, not a modern interpretation of what they did then.

Apart from the operational reality and safety being rudimentary at best, the objective was clearly just getting up and down again (safely being a nice extra) - what the point was (night interception? bombing?) remaining unaddressed.

There's a number of 'differences' to be borne in mind here, apart from spelling and the rule of the road; 1930s aviation developed from 'seat of the pants' to fundamental airways and night (not 'all weather') flying in the 1930s. I suspect that US, British Empire and continental practice all developed more or less independently; and 1930-1941 and 1941-45 were two different eras in terms of night flight.

In the '30 there was unwarranted optimism as to the utility of some types at night, the Spitfire Mk.I being expected to act as a day and night fighter, and thus being equipped with lights and signalling devices to allow that. It was far from ideal in the role. I suspect US types like the P-39 and P-40 had just as unrealistic expectations placed on them. It was only in 1940-41 when the RAF Bomber Command and Luftwaffe both switched to night missions that the systems started to be refined and more realistic for both bombers and their predators - although the P-61 was a case of overkill based on 1940 RAF data.

Cheers,

What I was trying to point out is this, on US aircraft, you see 3 colored lights for ID purposes. On th T-6, it is in the belly, on 51s, it is under the wingtip, on a 38, they are under the gondola. But, I have never seen the same 3 lights on any commonwealth aircraft, so using a Britsh pilots notes to explain the US 3 color light ID system does not work. If you can show me a Spit, Hurri, Lanc, Mosquito, with a 3 light ID system, then I will agree that the British notes can apply.

JDK · **Posted:** Fri Aug 15, 2008 9:45 pm

Indeed. I wasn't implying that.

The Demon notes were quite specific to that type in that era - perhaps even in RAAF use; my later comments were about the development of night flying operations, in general, and the need for lighting. At no point did I suggest that 'British' notes might apply, in fact I carefully pointed out that the same challenges were addressed (AFAIK) differently in the US, Continental Europe, and the British Empire - Russia was probably different again.

I don't know anything about the US system. However it's quite probable that the three light system was a air-ground recognition / signalling device, that being a common theme in the 1930s when these types first flew. Less likely an air-to-air one.

Because of the 1930s issues with wireless and voice radio other signalling methods were retained into W.W.II including Very / signal pistol ports etc; by the US, Britain Germany et al. It seems obvious that the downward facing ident lights were for recognition and possibly (intended but not used) for signalling. There were numerous 'good ideas' of the 1930s which had fixtures on aircraft that were rather like an appendix - remnants rarely if ever utilised. But I don't know about the US use.

Just some random thoughts.

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Recognition Lights and WWII IFF

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