The literal meaning of the noun tartan is: a woollen cloth woven in one of several patterns of coloured checks and intersecting lines, especially of a design associated with a particular Scottish clan.

This word has come to be also used allusively in reference to Scotland or the Scots—cf. Tartan gang.

In particular, the informal humorous term Tartan army denotes the fans of the Scottish football team, considered as a group.

The earliest instance that I have found is from the title of an article by the English journalist Basil Easterbrook (1920-95), published in the sports pages of The Journal (Newcastle upon Tyne, Northumberland) of Tuesday 18^th May 1971:

Wembley nightmare
Tartan ‘army’ invades again

To those only mildly interested in sport it must be a source of unending amazement that strife in most of its forms allies itself even to seemingly pacific pastimes like cricket and tennis. The quaint conception that sport leads to amity among nations is the funniest thing since granny caught her bodice in the mangle.
Having contemplated with no enthusiasm at all a trip to Belfast domestic international soccer for England’s opening game in the championship on May 15, I find little relief in the knowledge that one week later Scotland will be playing England at Wembley.

The wild men

That means that from Friday evening to early Sunday morning, 30,000 Jocks will be on the loose in London. If I had a maiden aunt in Penzance, this undoubtedly would be the week-end I should choose to pay her a visit.
Ian Wooldridge¹ once wrote “It’s a bit late now, but World War II need never have happened had they sent Adolf Hitler a couple of complimentaries for the England-Scotland soccer match — he would have crept home and realised there already was a master race. Mostly they are five feet tall, unintelligible of tongue, have chips on their shoulders, bells on their hats and carry an off licence in both overcoat pockets.”
I do not deny there is humour in the situation — but only if you are physically detached from it. To be caught somewhere along Wembley by a horde of tartan-daubed wild men and swept on towards the twin towers on the skyline is to know exactly what it feels like to be a would-be conqueror on his way to assault an embattled fortress. God help the amiable Sassenach who stumbles and loses his footing in such a situation.
I have not yet heard of anyone being trampled to death on the concourse, but two fans were killed when they fell, or were pushed, from the 10.30 out of Glasgow Central in 1949 on the night before Scotland won 3-1 at Wembley. Another soccer fanatic was discovered crouched on the running board; and yet another was found riding one of the buffers on the same train.
You remember some games better than others, naturally. I recall 1949 because it was the first time I reported an England-Scotland affair. I remember 1961 because England won 9-3, the record margin in the 99 years-old series. On that occasion John Rafferty wrote:
“After a night of revelry and little sleep they leave their bottle-strewn compartments in the grey dawn of Saturday, float into Euston station with the numb and detached feeling of New Year’s morning, half-slept, unshaven, damp-dry from paper towels in flooded toilets a miserable start to a day of glory.”
And after that — nine goals up their kilts! Dear Mother was it worth it?

Full of drunks

The one thing about staging this fixture in London every other year, which, war years apart, has been the case since 1924 is that at least the great amorphous sprawl of the capital can dilute and to a certain extent absorb the invading terror. Consider what it meant to a provincial town from the story the “Northern Daily Telegraph” of Blackburn² published when the game was staged at Ewood Park, in April, 1891.
“Blackburn has to put up with a good deal of noise and incipient blackguardism from the crowds following football teams who come to play the Rovers, but the horde of Scotsmen who poured into the town on Saturday morning put all records in these respects into a deep, deep shade.”
Space precludes me from quoting it in anything like the length it deserves, but at four o’clock the sleeping populace were awakened by “shrieking war whoops, riotous singing, accompanied by the crash of glass and the splintering of door panels.”
In King William Street, a stubbornly contested game of football was in full swing before 6 a.m. Hotels and eating houses were besieged and one wealthy Scottish sportsman who had ordered “Ham and eggs for 45„ at the leading hotel arrived with his friends for breakfast only to find that 45 ravenous brother Scots were bolting his party’s eggs and ham with what, in the journalistic style of the day, was described as “astounding celerity.”
Long before noon the cells were full of drunks and even more had to be left lying in the streets of Blackburn because the police had nowhere to put them. The writer concluded his account with the totally unnecessary observation—“Blackburn’s opinion of Scottish football enthusiasts is not likely to be a high one.”
It’s not life for a sensible English coward like me — looking over his shoulder for gunmen in Belfast one Saturday and getting ready to run from a bunch of Rangers and Celtic supporters on the one day in the year when they are united against the “Auld Enemy.”

¹ Ian Wooldridge (1932-2007) was a British sports journalist.
² Blackburn is a town in Lancashire, north-western England.

The issue of The Northern Daily Telegraph relating the above-mentioned story is not available online, but several newspapers quoted the article in its entirety; the following for example is from The Lanarkshire Examiner, and Upper Ward Advertiser (Lanark, Lanarkshire, Scotland) of Saturday 11^th April 1891:

The Northern Daily Telegraph, of Blackburn, says:—Blackburn has to put up with a good deal of noise and incipient blackguardism from the crowds following football teams who come to play the Rovers, but the horde of Scotchmen who poured into the town on Saturday morning put all records in these respects into a deep, deep shade. It is estimated that about 5000 men travelled by the excursion from Glasgow and Edinburgh, and they commenced to arrive as early as four o’clock in the morning. Soon after this hour sleeping townsmen were alarmed by shrieking war-whoops and riotous singing, accompanied in several places with the crash of glass and the smash of door panels. One tradesman in a principal street on drawing aside his blind to see the occasion of the blood-curdling tumult, was startled to perceive a “braw Scot” perched on the top of the pole supporting one end of his sunblind, and coolly smoking a cigar; while another gentleman was making vigorous efforts to climb up the other standard. Transfixed with astonishment, the tradesman was soon perceived by other men in the street, and he hastily retreated on a threat being made in an unfamiliar but unmistakeable tongue to perform the operation known in the Black Country as “’eaving ’arf a brick at ’m”. A minute afterwards sounds lower down the street indicated that ’arf brick had been ’eaved with disastrous result to a neighbour’s window. In other parts of the town—over which the visitors swarmed with remarkable rapidity—similar scenes were frequent. In King William Street a stubbornly contested football game was in full swing before six o’clock, every kick being signalised by a perfect storm of howls and shrieks. Isolated and wild-looking groups of strangers were also met with in out-of-the-way parts of the town, either making the early hours hideous with caterwaulings, or “punching” a football along the roadway with a perseverance worthy of a better hour. There were others, of course, who were not so noisy. The hotels and eating-houses were besieged long before their doors were opened, one coffee tavern having at least a couple of hundreds standing en queue on the pavement awaiting their turns. Some remarkable stories are told of the despair exhibited by the hungry Scots when they discovered that “parritch” was not, so to speak, on tap in Blackburn, and that to obtain any refreshment at all at least “saxpence” had to “go bang.” One gentleman ordered “ham and eggs for forty-five,” only to find, when he entered the dining-room of the hotel, that 45 other ravenous “brithers” were bolting his party’s eggs and ham with astounding celerity. It was many hours before the demand for food slackened, and there is good ground for the belief that many of the visitors, unable to get anything to eat, did double work with the crooked elbow. Long before dinner-time drunken men were staggering about the streets in all directions, and the accommodation afforded by the police cells was tested to the bursting point. At the railway station still more singular scenes occurred. As each of the trip trains arrived the porters had to clear out armsfull [sic] of whisky bottles, very few of which were quite empty. In one compartment alone, twelve full-sized whisky bottles were found of which three were quite full, four others about half-full, and the rest nearly empty. As the trains disgorged their contents, it was apparent that many of the passengers were too far gone to walk alone, but the railway people hardly liked the unanimous manner in which the unsteady ones took possession of all the seats and recesses on the platforms, and settled themselves for “forty winks.” When the platforms became inconveniently crowded in this manner the order was given to “move on,” and with much difficulty and a good deal of noise the station was at last cleared. But Blackburn streets in the early morning, and with rain pouring down, does not offer an inviting prospect to the shivering ones, and so it happened that scores of householders found drunken men asleep in their doorways and passages when they came down to breakfast. The market people naturally formed easy subjects for Scotch joking, in the forenoon, and for some time the humorous visitors made things lively for the stallholders, apples and oranges making good missiles with which to smite a fellow joker, and sometimes being big enough for footballs. Soon after midday the majority of the visitors went off to Ewood Pack to witness the football match, and the remarkable spectacle was witnessed of scores of Scotchman, in all stages of intoxication, sprawling on the seats of the stands, either asleep or sleepily quarrelsome. What happened after the match must be left to the imagination. The return train got away about midnight after scenes indescribable, many of the passengers having to make distressing spurts to cover the distance between the police stations and the railway in the short time allowed them by the guardians of the peace. Large numbers never caught the trains at all, but sitting asleep in the houses that gave them shelter in the evening, forgot their trains and their troubles until too late. Altogether, Blackburn’s opinion of Scotch football enthusiasts is not likely to be a high one.