In the 1918 election, Sinn Féin (the original Sinn Féin led by Arthur Griffiths, incidentally, like the SNP today, favoured* a dual monarchy) won 73 out of 105 Irish seats in the Commons - 69,5% of available seats. They won, incidentally and partially, because the British regime of the time reneged on a promise to deliver devo max.
The next month they convened the First Dáil to form a breakaway Irish government, and declared formal independence from the United Kingdom.
The Irish Republic had much of the machinery of State, just as Scotland does today: its central policy-making body was a unicameral parliament which elected a president of the ministry (Príomh Aire, or, in English, First Minister). He was answerable to Parliament and appointed the ministers.
Effectively, to exist as a functioning state, a state must have four fundamental internal attributes:
1. A parliament
2. A courts system
3. A police force
4. A constitution
The Irish republic had control of all of those - with Dáil Éireann, the Dáil Courts, the Irish Republican Police, and the Democratic Programme. Modern Scotland has three of these attributes, controlling the Scottish Parliament, the Scottish Courts Service and the Police Service of Scotland.
Before the creation of the Scottish Parliament, demands for independence were invariably met by the line from Unionists: "if you want independence, elect a majority of SNP MPs", a bar so impossible to clear as to be, deliberately, ludicrous. It's not so ludicrous today.
The point is - Scotland already has much of the functioning machinery of statehood. She has a pro-independence parliament. The British have already conceded the principle that if Scotland's people choose to be independent, so we shall be.
A pro-independence majority of Scottish seats, as in that far-off khaki election, would legitimise independence as never before.
If the SNP was to win a similar share of seats than the Sinn Féin romp which resulted in the creation of the Irish Republic, it would demonstrate to the world that independence remains very much on the agenda.
Clearly, the environments are entirely different. The British do not oppress Scotland as they did Ireland. There is no threat of looming war. The British have conceded the principle that they cannot hold onto countries against their will. And, despite the hysterical shrieking of the more unhinged fringes of Unionism, there is no prospect of the national territory being carved up and partitioned.
Forty-four seats would be an astonishing result for the Nationalists and difficult to achieve. It would be 75% of Scotland's seats - a supermajority in many national parliaments enabling those who hold it to change the constitution - higher than in 1918, and it would force the British, at a minimum, to concede at once the Home Rule the Scottish electorate were told they were voting for in May.
And if the British renege on their Home Rule promise as they did in 1914, then pro-independence majorities in both Holyrood and of Scottish seats at Westminster would perfectly legitimise a scenario where in 2016, Scotland goes to the polls to elect a parliament on a manifesto commitment of independence. A referendum is not the only way to independence.
* To avoid unnecessary diversion in the body of the post, a short explanation of Sinn Féin's attitude to the monarchy is this:
The original Sinn Féin, founded by Arthur Griffiths, who later became President, supported a dual monarchy, inspired by the example of Hungary, which had in the previous century moved from being part of the Austrian Empire to a separate, equal kingdom within Austria-Hungary, and which is potentially the very best example of the potential extent of Home Rule.
When Griffiths' Sinn Féin merged with republicans under Éamon de Valera (himself later three times Prime Minister), a compromise was reached between the monarchist Sinn Féin and the republicans that the new Sinn Féin party would pursue a policy of a republic in the interim, with voters later to decide on the exact form of government, subject to the condition that no member of the Windsor family would ever be invited to serve as monarch.
On independence, Irish leaders such as Kevin O'Higgins discussed retaining the monarchy in the long-term in return for the end of partition. This viewpoint went out of fashion after O'Higgins, the Minister for Justice, found himself assassinated.
Ultimately, when Ireland became independent, it was as a kingdom sharing a monarch with the United Kingdom, until the repulsion of the External Relations Act stripped George Windsor of all of his powers and transferred them to the new office of President.