NAA: MP1049/1, 1918/066, pages 674 through 690 is a copy of Directorate of Military Intelligence report HB56, 'Aircraft, lights and objects reported seen in the air -- summary and appreciation no. 3'. It is a continuation of the first such 'summary and appreciation' HB53 of nearly a week ago (no. 2 was an interim update issued on 30 April 1918; see NAA: MP1049/1, 1918/066, pages 694 through 699). It includes summaries (by my count) of 21 new mystery aeroplane reports made in that time, including several at Terrigal and Casterton, and some already discussed, West Footscray (no. 35), Mornington Junction (no. 43), Hunter's Hill/Cremorne (no. 51 -- an extraordinarily long summary, fully 2 pages instead of the usual few sentences), Newcastle (no. 52) and Cockatoo Island (no. 54). There are also updates on earlier cases, including Nyang and Ouyen (based on the investigation made by Sickerdick and Edwards); Terrigal ('there is a small beach near TERRIGAL where a seaplane might land'; written comment: 'Why should a seaplane land on a beach?'); Macarthur ('The spot on which an aeroplane was reported to have landed has been visited and has been found to be a most unsuitable place for a night landing'); Toora ('The informant is reported to drink heavily and consistently').
So it seems that scepticism is beginning to set in. Some of the 'appreciation' (geographical and temporal distribution, even the number of bases) has not changed since HB53. But then there is a section headed 'Improbability of some of the reports':
The number of reports is now so great that it is very difficult, assuming that all are true which have not been proved to be false, to attribute them to flights either from vessels at sea or from land bases.
That is, even if it is assumed that all remaining reports are true, there are still so many of them that it just strains credulity to attribute them to covert enemy activity:
If flying is occurring on the scale which these reports suggest, it might be expected that there would be occasional forced landings as well as the voluntary landings which the truth of these reports would presuppose; but not a single instance of a landing has been established [...] Further, no traces of the organisation which would be necessary to maintain aircraft in order have been discovered.
So, 'it is improbable that all the reports are true'. The conclusion drawn from this is not that all of the reports are of no consequence and should be disregarded, however; what needs to happen now is 'to winnow the grain from the chaff' before further 'discussion' can take place. So it's still possible that there could be German aeroplanes flying over Australia; but the true numbers have been exaggerated by false reports and needs to be properly established.
The rest of HB56 begins this winnowing. Some reports are dismissed because the witnesses are 'probably unreliable', including those from Toora and Christmas Hills; others because they contain 'details not consistent with the flight of aircraft', including West Footscray. Then there are those which 'have been shown to be almost certainly without foundation, or to be explicable as due to other occurrences than the flight of enemy aircraft', including Macarthur. A number of reports based only on hearing (and not seeing) aircraft can be regarded as 'probably without foundation' and not requiring further investigation:
Even people accustomed to aircraft sometimes mistake the sounds of motor cycles and other motor vehicles for those of aircraft. Other sounds which might mislead persons not accustomed to aircraft are those of flights of birds and meteorites.
But also, reports of 'an aeroplane or other object showing lights should not be accepted as sufficient evidence':
Night flying is dangerous, and aircraft flying at night usually keep at a great height. Aircraft do not usually show lights, except when about to land, and hostile aircraft not wishing to disclose their whereabouts would be especially careful not to have lights.
Especially, 'An appearance of oscillating movement may be given by the scintillations of a star':
A case is on record at the Melbourne Observatory of a clergyman who was on the summit of MT. DANDENONG on a clear night when the Orion stars were rising. He took them for aircraft and reported them as such to the Observatory. This was before there were any aircraft in the Commonwealth.
(This must be a reference to the 'beautiful revolving lights' seen by Reverend Cozens during the 1909 mystery airship wave; so somebody at the Observatory has been paying attention.) So the reports from Terrigal, Maffra, Walpeup, West Footscray and Mornington Junction, among others, 'may therefore be regarded as not established and probably without foundation'. A final class of explanation is that the sightings were of birds:
In the United Kingdom the air service has frequently received false but honest reports of aircraft due to birds having being seen. Even at the front, it is of-ten difficult to distinguish birds from aircraft.
(Again, this is interesting because it shows an awareness of parallel phenomena in wartime Britain.) As an example, an October 1914 report from a 'battery of [coastal] artillery' at Brighton, Tasmania, is quoted:
The aircraft were firing smoke balls, usually in series of 3 or 4. It is difficult to accurately estimate the number of aircraft operating, I personally saw eight separate series of smoke balls firing almost simultaneously and at such wide intervals that it was impossible for them to have fired them by the one machine. The smoke balls fired at first were seen to be small dark puffs which quickly swelled to thick circular puffs of dense black smoke quickly elongated and dissolved by the wind.
But 'In fact there were no aircraft, and the "puffs" were probably the sudden scattering or turning of flights of birds'. The reports from Nyang/Ouyen, Grafton, Hunters Hill/Cremorne and Newcastle are among those which probably fall into this category.
So what is left? There's Terrigal, on the NSW Central Coast, where the earliest reports have now been discounted, but not the seven more recent ones; 'Special inquiries are being made in this district'. There are also ten or more other reports where there is not yet enough information to make a final determination. Some already look doubtful, such as Nelson (which 'seems improbable, but cannot be finally dismissed'); others are a more intriguing, like the piece of metal found at Ballarat West 'which appears to be part of the casing of a [signal or firework] rocket'.
In the end, even though 'this criticism suggests the probability that most of the reports are unreliable or do not relate to aircraft', HB56 does not recommend wholesale scepticism. Even the dubious ones 'must be kept on record and considered with any later reports that are received'. And while it is recommended that a 'competent naturalist' be brought in to assess daylight reports, 'It should be remembered too that just as bird can be mistaken for aircraft, so aircraft can be mistaken for birds'.
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