Units on ASIs of WW2 bombers

As an ex, post war trained, nav, this is a fascinating thread.
For my threepennorth it depended on the chart/map used. It was common practice to use the Ordnance survey maps scaled in miles in the early days for map reading. However Mercator projection navigational charts were drawn up using Latitude and Longitude. This is far more convenient for navigation, i.e. Long lines are parallels and so lines drawn straight on the chart maintain a constant bearing, and, equally important, one degree of Lat is 60 nautical miles, so making measuring distances simple.
I am amazed that it took the RAF so long to change over from mph to knots, perhaps it was the perceived slight of taking orders from the Senior Service that upset their touchy sensibilities.

And really finally this time …

When I started this thread over a year ago I assumed that mph was the standard unit of speed during the early years of WW2, but that this changed to knots during the latter stages. I was attempting to find out when this change took place.

However, from the many replies it became clear that both knots and mph were in use at the same time – which seemed a strange state of affairs to a non-aviator.

It now transpires there was no standard procedure for much of the war. This from AP1234 (“Air Navigation”), Chapter 1, paragraph 62:

“It is immaterial whether the ground speed is measured in mph or knots, though it is customary to adopt the units in which the airspeed indicator happens to be calibrated. Many navigators prefer to use knots at all times, since the nautical mile is more convenient than the statute mile as a unit of distance when employing astronomical methods of navigation.”

Followed by paragraph 63:

“As a general rule the wind speed given by meteorologists is in mph unless specifically asked for in other units. The navigator may, however, measure the wind speed in whatever unit is most convenient to him.”

It wasn’t until 12 April 1945, and the issue of Air Ministry Order A.365/45, that mph was consigned to history with the adoption of the knot as the unit of speed (see my post No 24).

Brian

And finally …

The RAF Museum has just sent the following:

Air Ministry Order A.365/45 dated 12 April 1945 states:

“1. It has been decided to adopt the knot and nautical mile as the
standard measurements of speed and distance throughout the Royal Air
Force.

2. These measurements are already in use in Coastal Command. They were
adopted in Bomber Command from 1st April, 1945. Instructions for their
adoption in other commands will be issued by the Air Ministry when
circumstances make it convenient and practicable to do so.”

Presumably the circumstances relate to the availability of air speed
indicators calibrated in knots. Pilot Officer Prune used to boast that
“We were flying so low over the sea that our ASIs read knots…”

It is known that some Lancaster squadrons were still using mph ASIs up to at least the end of April 1945, so the reference in 2 above to other Commands adopting knots ” .. when circumstances make it convenient …” obviously also applied to Bomber Command, especially as the Order was promulgated 12 days after it was supposed to come into effect.

Brian

Many thanks Don – that’s exactly what I was looking for.

Brian

Brian
PS. Doesn’t anyone know anything about the Halifax?

The what? Halifax? Never heard of it. I do know the Lancaster and Spitfire though…….:p;):rolleyes::diablo::dev2::):)

Cheers

Cees

Don’t forget Max that Jim has also found that a number of 6 Group squadrons flying Lancasters were definitely working in mph/statute miles up to the end of the war. The whole of 4 Group was still flying Halifaxes at the time and, unless their ASIs had been modified, they would have been using mph etc.

I don’t think one should take Hoare’s statement as all-embracing – you yourself have just noted you have a navigator’s chart from March 1945 scaled in statute miles.

Trying to summarise what has been written here, and what has appeared in the Lancaster Archive Forum, it seems that at the beginning of the war the ASIs of all Bomber Command’s aircraft, including Lancasters when they started to come on line, were calibrated in mph and forecasts were presented accordingly. There is no doubt that this situation continued until at least March 1944.

At some time during the summer of 1944 some of the later Marks of Lancasters reaching squadrons were equipped with ASIs calibrated in knots. The navigators of these would have no option but to use knots and nautical miles in their calculations, but this was not universal practice since some Lancaster squadrons never converted.

In other words there was a right mixture of procedures – just as well the HSE wasn’t around then.

Brian
PS. Doesn’t anyone know anything about the Halifax?

That’s a very interesting diagram. The wind speeds are surprisingly high (or maybe they are not at 20,000 feet?) considering a bomber would be cruising at about 210 – 220 mph.

Do you know how the winds were actually measured by the winfinders? I’ve never really given it much thought but were they using ground references visually, or by using H2S, or were the winds calculated when the bombers were still in range of GEE?

That’s a good question which Brian has already had an input in contributing his knowledge on other forums….I’m hoping to get the “definitive” answer from my nav. contact shortly!
Max

Brian, regarding navigator’s charts, I have a copy of one for the Ladbergen raid on 3 March 45 and it clearly states on it “statue miles”. You may also be aware that Jim Cave (and I) are in correspondence with Peter Hoare who was a nav. on 83 PFF squadron at Coningsby. He has stated that during late 44 and 1945, air speeds were measured in knots, but the conversion from mph to kts was not a straightforward one! More to come from Peter on this topic but I have an article that he wrote decribing the Bohlen operation on 5 March in which he says “The route to the target 729nm consisted of nine legs…..” and later on “our planned IAS to this point was 150kts, which gave us a TAS of 184kts…” It kind of answers my original question on Lanc-Archive because Gus Belford was writing about exactly the same operation and he was using kts in his description.
Regards
Max

I think, but I’m happy to be corrected, that in this instance the aircraft were out of the range of GEE for the latter part of the leg, but H2S would have come into its own on reaching the Danish coast.

The winds are nothing unusual for 20000 ft. In this case the winds are those actually measured by windfinders.

Brian

That’s a very interesting diagram. The wind speeds are surprisingly high (or maybe they are not at 20,000 feet?) considering a bomber would be cruising at about 210 – 220 mph.

Do you know how the winds were actually measured by the winfinders? I’ve never really given it much thought but were they using ground references visually, or by using H2S, or were the winds calculated when the bombers were still in range of GEE?

I think, CD, that it should be remembered that the broadcast winds were not simply for navigation but an attempt to keep the bomber stream together so that it arrived over the target as near as possible in a compact formation.

Although the windfinders were all supposed to be experienced navigators there was, no the less, a considerable scatter in the winds they sent back to HQ Bomber Command via the Groups. The forecasters then had to decide which to disregard then compute a mean from the remainder. This wasn’t for just one level but sometimes 4 or 5 and the time available was limited.

At HQ Bomber Command the found winds were plotted on a vector diagram so the winds that were seriously in error were obvious, but even so there could be quite a spread. I’ve reconstructed one of the vector diagrams using found winds reported on a Berlin raid on the night of 28/29 Jan 1944 to show what I mean. This was before the foun/broadcast wind procedure was introduced and was actually a trail to see if it had merit. The blue Z is the mean wind calculated after the event by the Command Nav Officer.

As a matter of interest on this particular operation one aircraft often reported winds 90 deg different to the others.

It is easy to imagine how, if all the aircraft on an operation depended on their own navigator, the stream would become scattered.

(Hope this works, I’m not used to posting attachments.)
Brian

Windfinders sent the found winds to their Groups within brief, fixed, time frames; the broadcast winds, based on the found winds, were broadcast shortly after within similar brief time frames. So far as I’m aware only one unit was used, mph.

I’m far from an expert in navigation but I would guess that doing the conversion between statute and nautical miles was trivial compared to the actual job of navigating a bomber over hundreds of miles of blacked-out airspace. From what I’ve read the broadcast winds were often inaccurate and the 15% difference between statute and nautical miles would surely not have been that significant considering other errors.

Graham and CD,

You’ve both hit the nail on the head – that if some crews were using knots and others mph, then if the broadcast winds were in mph, this was a recipe for considerable error – if not the sort of tragedy that CD describes.

Windfinders sent the found winds to their Groups within brief, fixed, time frames; the broadcast winds, based on the found winds, were broadcast shortly after within similar brief time frames. So far as I’m aware only one unit was used, mph.

If all the bomber ASIs were in mph it seems logical that wind forecasts would have been in mph until such time as the majority of aircraft were equipped with ASIs in knots.

One would have imagined that as increasing numbers of the later Marks of Lancasters reached operational units then knots would have become the preferred unit, but even at the end of the war this appears not to have been the case. The 6 Group Navigational Summary for April 1945 makes specfic reference to excellent navigational results by 419 and 428 Squadrons (both flying Lancaster B.Xs) and adds:

“It might be noted too, that these squadrons are handicapped in that, not having converted to knots, all calculations were made in mph ….. “

(The above courtesy of Jim Cave)

So we are left with the odd situation that some crews were using knots, some mph – and a sense of wonder that any operation met with success.

Incidentally we’ve still two ananswered questions:

1. Were the ASIs of later Halifax Marks in mph or knots? (The Order of Battle for 6 May 1945 shows 17 squadrons still flying Halifaxes).
2. Were navigation charts scaled in nautical or statute miles?

Brian

Probably an apocryphal story but I remember reading somewhere that during the war when RAF Spitfires were being flown of a RN carrier to Malta the range that the Spitfires could manage was given to the FAA planners. When the carrier was within that range the Spitfires were flown off…

…unfortunately the RAF had given the range in statute miles and the FAA were used to working in nautical miles. The result being that most of the Spitfires ran out of fuel before they reached Malta.

This incident was given as the reason for the change to nautical miles (and knots) for all British aircraft.

Thats an interesting story and probably not the only accident that occured because of the difference between the nautical mile and satute mile. How easy would it be for a Spitfire Pilot flying a Seafire to make any number of speed related fatal mistakes. Thanks for the info on Bomber navigation.

HiGraham
I also was under the impression that most of the changeover to kts was post war,but we are here to learn !!

regards baz

We are indeed 🙂

Another question that occurs is that werent there master bombers in the stream that everyone followed? Possibly the Squadron Leaders aircraft did the navigation and everyone else stayed in formation?

No, the job of Master Bomber was to direct the bombing at the target by giving a running commentary about the accuracy (or not) of the Pathfinder marking flares / target indicators.

All Bomber Command night bombers flew to the target completely independently but along a pre-planned route. Navigational assistance (apart from radar / radio aids) was limited to wind-speed information that had been measured by special ‘windfinder’ bombers which was radioed back, averaged, and then re-broadcast to the main bomber stream.

Probably an apocryphal story but I remember reading somewhere that during the war when RAF Spitfires were being flown of a RN carrier to Malta the range that the Spitfires could manage was given to the FAA planners. When the carrier was within that range the Spitfires were flown off…

…unfortunately the RAF had given the range in statute miles and the FAA were used to working in nautical miles. The result being that most of the Spitfires ran out of fuel before they reached Malta.

This incident was given as the reason for the change to nautical miles (and knots) for all British aircraft.

HiGraham
I also was under the impression that most of the changeover to kts was post war,but we are here to learn !!

regards baz

Graham and Bazv,

Many thanks for your replies.

I’ve done some research on this from a Met Office viewpoint and the raw data on which forecasts were based. At the beginning of the war winds aloft were recorded as kph, but this changed to knots at the beginning of 1944. Logically, as far as the Met Office was concerned, wind speeds would have been forecast in the units in which the raw data were received, but there is no doubt that up to and during the first months of 1944 forecasts were in mph and any references to distance were in statute miles (AIR2/5029).

Forecasts would only have been issued in mph if that was what the customer, Bomber Command, demanded – thus the conversion from kph/knots to mph was done by the Met Office – not the aircrew.

I’m sure that the requirement for speeds to be presented in mph was solely because all the aircraft I listed in the first post of this thread had ASIs reading mph – given the number of restoration projects and specialists on this forum it has been rather disappointing that none of those involved could answer what is really a very simple question.

I’m equally sure, but don’t know, that when the really large raids (in terms of numbers of aircraft) started in 1942 all the ASIs were calibrated in mph but, as you state Graham, in the later Marks of Lancasters this changed to knots. However, did the same happen with the Halifax or did the ASIs remain in mph to the end?

Reading through this I suppose, Graham, I’m really repeating what you’ve already said, but the ramifications are considerable if a couple of navigators erroneously used mph instead of knots, or vice versa, in respect of time on target or ‘simple’ navigation.

Brian

Brian

Your met office info is interesting and seems to confirm that the bomber streams used MPH ASIs until at least mid 1944. I am surprised the info comming out of the met changed as early as the beginning of 1944 I would have thought it would have been later considering a good many aircraft did survive for prolonged periods and would have carried their original instrumentation ie MPH. I have a good many Bomber type MPH gauges dated 1944 and later and thought the change over on land based aircraft to knots happened mainly post war when MPH all but dissapears.

I think being British built you have to assume that Halifax were fitted with MPH on this basis.

Another question that occurs is that werent there master bombers in the stream that everyone followed? possibly the Squadron Leaders aircraft did the navigation and everyone else stayed in formation? I think its almost certain that in the 1000 Bomber raids some of the aircraft will have ASIs in knots as FAA and other commands contributed aircraft to make up the numbers.

Perhaps this explains why so many aircraft ended up off target. Navigators trying to convert info in MPH back to knots?

Found this info on the MK X

Of later variants, only the Canadian-built Lancaster B X, manufactured by Victory Aircraft in Malton, Ontario, was produced in significant numbers. A total of 430 of this type were built, earlier examples differing little from their British-built predecessors, except for using Packard-built Merlin engines and American-style instrumentation and electrics

Its certainly an interesting mystery.:)

Looks like (as usual) no simple answer !
What I was alluding to (badly) in my earlier post was –
were the navs using charts scaled in nautical miles or statute miles ??
Nautical miles are surely easier for navigation ??
still no thread drift 😀

regards baz