Origin of the term 'Pom'

Solution 1:

According to World Wide Words, the theory about the pomegranate seem to be the more credible one, its real origin remains unclear for this outdated term:

• Part of the reason for all these theories growing up is that there was for decades much doubt over the true origin of the expression, with various Oxford dictionaries, for example, continuing to say that there is no firm evidence for the pomegranate theory. That origin was described by D H Lawrence in his Kangaroo of 1923: “Pommy is supposed to be short for pomegranate. Pomegranate, pronounced invariably pommygranate, is a near enough rhyme to immigrant, in a naturally rhyming country. Furthermore, immigrants are known in their first months, before their blood ‘thins down’, by their round and ruddy cheeks. So we are told”. You will note that he had to explain the pronunciation that we would now take to be the usual one: in standard English it used not to have the first “e” sounded, with pome often rhyming with home.
• It is now pretty well accepted that the pomegranate theory is close to the truth, though there’s a slight twist to take note of. H J Rumsey wrote about it in 1920 in the introduction to his book The Pommies, or New Chums in Australia. He suggested that the word began life on the wharves in Melbourne as a form of rhyming slang. An immigrant was at first called a Jimmy Grant (was there perhaps a famous real person by that name around at the time?), but over time this shifted to Pommy Grant, perhaps as a reference to pomegranate, because the new chums did burn in the sun. Later pommy became a word on its own and was frequently abbreviated still further. The pomegranate theory was also given some years earlier in The Anzac Book of 1916.
• Whatever your beliefs about this one, what seems to be true is that the term is not especially old, dating from the end of the nineteenth century at the earliest, certainly not so far back as convict ship da

Pom:

• British person): Australian from 1912. contraction of pomegranate, rhyming slang for immigrant (“imme-granate”).

• The older term of Jimmy Grant, meaning immigrant, became Pommy Grant as the Australian sun allegedly turned immigrants′ skin pomegranate red.

• Folk etymologies also exist, for example:

  • A devolution of “Prisoner of His/Her Majesty” or “POHM”;
  • An acronym for “Prisoner of Mother England”.
  • An acronym for "Permit of Immigration".

(Wiktionary)

Solution 2:

Growing up in Australia (Sydney) in the 1950s, I remember being told by several older people whom I can't remember that the word came from the French word "pomme" for apple. The reason given was similar to one of the explanations for "pomegranate" as the source: English migrants tended to sunburn upon arrival in Australia. Another reason I heard was that when in England the cheeks of the English looked red like a red apple because it was so bloody miserable and cold there.

Despite the lack of corroborating made-up evidence on the internet, "pomme" seems a more plausible origin than "pomegranate", rhyming slang notwithstanding. I never heard of a pomegranate in Australia in the 1950s and 1960s, and it's still mostly an imported fruit. It would have been relatively unknown in Australia in the early 1900s. Many Australians fought in France in WWI and spent time in England before or after (e.g. my grandfather). The term seems to have originated around then. There was a lot of migration from England to Australia after the war so there would have been a lot of overlap of soldiers returned from France and England with English migrants. This etymology may have passed from my grandfather to my father to me.

For what it's worth.

Solution 3:

Early Australian newspaper instances of Pommies suggest that the expression originated in Perth, Western Australia. At any rate, the earliest mentions—totaling several dozen—of the term that appear in a search of the Trove (National Library of Australia) database of historical Australian newspapers are from that city. Here are twenty of them.

From Jean Dell, "Sleeping Out: Dame Nature's Free Lodging: A Night on the River Bank," in the [Perth, Western Australia] Sunday Times (January 21, 1912):

Also we were advised to this effect: "Beware of the Pomegranate Johns (immigrant policemen). If they catch you asleep it's odds on them putting the boot in. The local chaps are all right. They do give a man a chance. Although this is a public recreation ground, some of the Johns won't let the hard-up people use it, especially at night. There's one bloke comes down here who's a fair nark. We don't understand his language too well, him being a 'pommy,' but he lets us know what he means all right. Shifts us on every time he spots us, and if we didn't get away quick and lively he'd be sure to vag us, or let us know what English leather is like. This is a free country, I don't think."

...

"How do we pull through? Well, I don't know. Perhaps something turns up. You've got me beat there. We don't feel it while we're asleep down here. That's the best part of it, only for the 'pommy Johns.'"

From a letter by "BRITISHER, NOT BLACKLEG" (dated January 25) to the editor of the [Perth] West Australian (January 27, 1912):

Sir,-As "Another Britisher" does not seem to understand why the average Australian is so hostile towards the immigrant, or "jimmigrant," or "pommy," whichever name pleases them best, I should like to give him just one instance as to the cause. On Monday, January 15, the whole of the aerated water factories’ employees in Perth and suburbs ceased. There appeared in Tuesday’s paper an advertisement for between 100 and 150 men to take their places, and at 7.30 a.m. crowds of the immigrants who had arrived a few days previously could have been seen hanging round the gates of the various factories, well knowing they were going “scabbing” and “blacklegging” and were utterly ignorant of all the work, and were going to do a thing which they knew would not do in their own country. I was an immigrant two years ago, and must say that I am ashamed to own that section of Britishers as my fellow-countrymen. Perhaps “Another Britisher” can understand why.

From a letter by "A MOTHER" (dated January 30) to the editor of the [Perth] West Australian (February 3, 1912):

Sir,—Might I, through the columns of your paper, ask a favour from a few of the men about town? Will they please refrain from using insulting remarks to the girls and women who come from the old country, where they are always respected; while here we are afraid and too disgusted to walk out alone. It would be a real blessing to us if some friend would kindly take this matter up. We only come into this country to work for the good of the country, ourselves, and those that employ us. And when we take a walk after our daily work is over we don't like to hear these remarks: "Look at the dirty Pommies," which we are not; we are clean-living and clean-minded human beings, and we ask to be treated as such.

From "Notes and Comments" in the [Perth, Western Australia] Sunday Times (February 4, 1912):

Immigrants are known in Perth as "pommies." On the Golden Mile they are called "Jimmies." Why these distinctions?

From "'So Long, Saturday Night': Farewell to a Time-Honored Institution" in the [Perth, Western Australia] Sunday Times (February 4, 1912):

It is getting late, and the trams are rushed. Impossible bundles are forced on the platforms. The "pommy" conductors are protesting in patois resembling the Tower of Babel. The late-supper crowd stream into the haunts of stout and oysters. The hotel bars swarm with noisy good nature.

From "The Busker," in the [Perth, Western Australia] Sunday Times (February 4, 1912):

"The Coming of the Immigrant," screened at Spencer's Esplanade this week, is the advance-guard of the Australian Industrial, and as an initial attempt it will do, although we can't say that it is IT. The views of old-established wheatfields, with thousands of pounds' worth of horseflesh and harvesters careering up and down, ivy-clad homesteads, and Government experimental farms should go far towards kidding the potential pommy to rush wildly for his steerage ticket in the hope of grabbing a slice of this wilderness while the wild corn is yet ripe, and before the wild beasts of the jungle have had time to eat it bare. Tree-falling, per bio., likewise appears to be a rather innocent process, where a silent axe topples tough salmon over after two clouts. There are various other discrepancies, but we don't want to be a nark.

...

The moonlight effect in Spencer's "Immigrant" film, showing the pommy tramp coming into the Fremantle Harbor, is easily the best piece of local work done to date.

From "The Busker," in the [Perth, Western Australia] Sunday Times (February 11, 1912):

"The Coming of the Immigrant," locally screened by Spencer, was responsible, for a huge surge of big footed tourists to the Esplanade Gardens. Two thousand square feet of fresh tan was pulped to powder under the mighty pressure of pommie.

From "They Say" in the [Perth, Western Australia] Sunday Times (February 11, 1912):

That at latest the old man is trying to swear in the pommy gardener as a special constable.

...

That a newly-arrived pommy made a monkey of a bunch of tormentors and slingers-off.

From "The Busker," in the [Perth, Western Australia] Sunday Times (February 18, 1912):

"Gold Mining in W.A.," at Vic's Pictures, Fremantle, gives the newly-arrived pommy something to lean his brains against. Out of the common is this picture, inasmuch as not one of the hundreds of miners employed appears to be aware that the bio. camera is on hand, the underground workings being perfectly photographed.

From "Notes and Comments" in the [Perth, Western Australia] Sunday Times (February 25, 1912):

The great Australian slanguage is becoming remarkably rich in synonyms. Immigrants are variously known as "jackeroos," '"pomegranates" and "pommies." Non-union men are called "scabs," "blacklegs," "zambuks" and "zams"-the latter in delicate allusion to the preparation which is advertised to remove scabs. Canting parsons are "tub-thumpers," "Holy Joes," "devil-dodgers" and "wowsers."

from "Verse and Worse," in the [Perth, Western Australia] Sunday Times (February 25, 1912):

"Is Gus your landlord where you live?" demanded the constable, signalling to a team man not to run over a couple of half-baked pommies staring at the Town Hall clock. "Come on," he demanded, "tell me your address."

From a classified advertisement in the [Perth] West Australian (March 1, 1912):

WANTED, Yardman, must be good milker, no pommies need apply. Love Bros., Belmont.

From a letter by "A.M.R." (dated March 6) to the editor of the [Perth] West Australian (March 9, 1912):

These recent arrivals do not come here as poverty-stricken outcasts. They have left an older civilisation where, doubtless, opportunities are fewer, and the battle of life more strenuously waged. They have come in hopes of finding a wider field and they only ask a fair field and no favour. I say that it is the bounden duty of those who are responsible for their presence here to see that they have this fair field, and for these same authorities to come down with a quick and a heavy hand on any mean-spirited individuals who would dare to offer the strangers these dastardly insults. The other day I noted a tradesman's advertisement for lab our which concluded with the truly manly phrase, "No pommies!" With what pleasure I should have informed that tradesman when he called for his orders next day, "Thank you; you may discontinue your calls on me in future. I like someone more broad-minded and manly." If this jealous, inhospitable spirit is allowed to continue Western Australia will stand disgraced in the eyes of every honourable, fair-minded man.

From "The Australian 'Slanguage': Its Graces and Peculiarities: Expounded by 'Tuck'––for the Benefit of New Arrivals," in the [Perth, Western Australia] Sunday Times (March 10, 1912):

When the tribe of pommies, jimmy-grants, and unregistered lime-juice lickers hears a native of the soil—who is a groper—refer to them in any of the following terms, a "boshter," "bontodger," "bonza," "boshterino" or "bosker" bloke, he need not go sour and agitate his Lancashire clogs with the intention of kicking the spruiker of this chat in the "darby kell" because all these expressions represent the dead limit of admiration.

From "They Say" in the [Perth, Western Australia] Sunday Times (April 14, 1912):

That a tram ride in Perth was recently enlivened by a battle royal between Gripers and Pommies.

That before the car had left the city end the native-born produced beer and challenges.

That the immigrants and their families replied in sulphurous kind to the comments.

That the tram men ended the barney by heaving the combatants off the car.

From "'Aliens' and 'Natives'," in the [Perth] West Australian (April 15, 1912):

How far this sense of oneness goes is seldom realised. A striking indication was given the other day in a big departmental store in the city, when a Chinese lady on the trail of one of the errors that afflict housewives, blamed a "pommy" for the fault, and insisted that more care should be taken in admitting newcomers to "our country" in competition with "our own people." The members of the A.N.A. will be the first to recognise how remarkable a proof this affords of the extension of the national sentiment they have done so much to create, among a race notably unwelcome in the Commonwealth.

From Daisy Bates, "Our Immigrants," in the [Perth] Western Mail (April 20, 1912):

We hear a poor immigrant utter a few words in his provincial dialect, and "Johnnie" or "pommie" is flung at the poor, bewildered newcomer! Well, perhaps in the end it will serve a good turn, for if in the course of time Johnnie or "pommie" rises to Parliamentary and Cabinet rank he will, remembering the jeer, make it easier for the newcomer his Government is inviting and welcoming.

From "The Young Guard" in the [Perth, Western Australia] Sunday Times (April 21, 1912):

We notice that the authorities are crying out about shortage of registrations. We wonder if they ever take the trouble to rouse up any of those newly arrived immigrants eligible for service? Many of them are practically ignorant of the defence laws, and others (worse still) appear determined to evade service if they can, and to have no intention of registering voluntarily. Writer has met a few of these contemptuous "Pommies," and there are doubtless more to be raked up if the authorities like to trouble. Isn't it just about time something was done regarding these and the hosts of other lads who have not yet registered?

From "Notes and Comments" in the [Perth, Western Australia] Sunday Times (April 21, 1912):

The newly-arrived "pommy" is exceedingly partial to fruit. The day that an immigrant ship arrives is a day of rejoicing among the vendors of grapes and apples, for the junk-jaded strangers besiege the barrows and swarm into the shops until their fruit hunger is satisfied, You may know the lad from Lancashire by the apple that he munches. His track through the dense forest that extends from Perth station to the Immigrants' Home is littered with skins and cores. Incidentally the sight of twenty or thirty green-capped immigrants taking large bites out of Jonathans and Cleopatras adds a pleasing touch of rusticity to Hunter's Corner.

From "Notes and Comments," in the [Perth, Western Australia] Sunday Times (May 26, 1912):

The coming of the immigrants has enriched the great Australian slanguage, if it hasn't done anything else. In Perth the newcomers are known as "pommies" (a contraction of "pomegranates"), on the Golden Mile as "Jimmigrants" and "Jimmies," and beyond the Bight as "immies." Wonder which (if any) of these terms is "salted for perpetuity," like "Jackeroo" and "boshter."

Several of the earliest newspaper notices of the term Pommies explicitly tie it to the word pomegranate. I see no reason to doubt that linkage—although, disappointingly, these early mentions don't explain why native Australians made the connection between newcomers from Britain and the red-skinned fruit.

It seems exceedingly likely that popular usage of the term originated in Perth, Western Australia, since a very large swarm of early instances of the expression appear there—starting in January 1912—before the term appears anywhere else.