In terms of actual support, the Germans provided very little for the Irish Revolutionary Brotherhood (IRB) or other Irish nationalist groups during the war. The most concrete level of support was the smuggling of some 900 Mauser rifles in July 1914 from the schooner Asgard, but this gun-running operation had its inception before the outbreak of hostilities. The Protestant Ulster Volunteer Force (UVF) had already acquired a large arsenal of weapons in light of the worsening situation surrounding Home Rule in 1913/14 and by the time of the Asgard operation had imported approximately 20000 weapons. The UVF weapons were decidedly more modern than Mausers acquired from Germany, which dated back to the 1870s and were heavy, black powder rifles. By the estimate of one British intelligence report in 1916, the IRB and the Volunteers had around 11000 rifles, while the UVF had over 50000. To make matters worse for the would be insurgents, their arsenals were a heterogeneous mixture of German, Italian, and British weapons. Most of these were acquired from various sources ranging from American and German money to buying Lee-Enfields from British garrison troops.
The extreme disparity between the IRB/Volunteers and the UVF, to say nothing of the British Army, was in part a reflection of the relative disinterest the Germans had in supporting an Irish insurgency. Sir Roger Casemate and a revolving door of Irish revolutionaries made their way into Germany in 1914 in the hopes of securing German assistance for a rising, but their German hosts seldom paid more than lip service to supporting the Irish cause. Casemate often tried to sell the Germans on the strategic importance of an independent Ireland, but neither the Kaiserliche Marine nor the Foreign Office was much interested in offers of naval basing. British naval superiority ruled out a German landing and made running heavy arms to the island quite difficult. After much prodding, the Germans agreed to send in a shipment of 20000 guns an some heavy weapons on a German steamer masquerading as the neutral Norwegian ship Aud, but Casemate was not impressed. He wrote in his diary on March 1916:
A masterpiece of idiocy that admits of only one explanation. That explanation is clear. The German Government want to bury the "folly" of the [Irish] Brigade, the Treaty & all their coquetting with "Irish rebellion" in this paltry gift of 20,000 rifles, leaving us to bear the shock and pay the piper and they want bloodshed in Ireland.
My view is that we should try & get the guns across. If we don't do that we run counter to the strong wish of those at home and in America who are counting on this at least. The guns, if landed, are an asset & to merely land them need not necessarily involve any bloodshed, or serious trouble, if the men in Ireland can act well.
Casemate's tart dismissal of German "coquettishness" towards Ireland had a good deal of merit. The 20000 guns on the Aud were captured Russian rifles, which the IRB/Volunteers would have had a difficult time finding ammunition for during a rising. The Mosin–Nagant rifles were an expendable asset that the Germans did not have any use for, and thus surplus to German military needs. Casemate returned to Ireland via a u-boat, but despite pledges to German Chancellor Bethmann-Hollweg of the Irish Brigade's commitment to the side of the Germans, there is some evidence that Casemate wanted to prevent the Rising. Aud's cargo was significantly less than what Casemate requested and his diary reveals that his hopes for a successful revolt were nil. His diary entries show he saw the Russian rifles as a German attempt "to get rid of us...on the cheapest possible terms to themselves." Whether or not Casemate could have persuaded the IRB/Volunteers' leadership to simply store away the guns for another day was rendered moot by the Britain's quick apprehension of both the Aud and Casemate. The Rising thus had to make do with the motley assortment of weapons it had already acquired.
This is not to say that Germany's role in the Rising was completely nugatory. Although Germany provided at best minimal assistance to the Rising, the presence of Germany on the horizon added a charged dimension to the Rising that would not have been there had it not taken place in midst of a world war. The war lent Irish affairs a much more global quality and made real the tantalizing prospect of a great power backing the Irish cause. Reportedly when Seán Mac Diarmada heard of Franz Ferdinand's assassination, he excitedly saw this as the IRB's time to strike. Planning for a rising, which once seemed hypothetical, began to take on concrete support with the promise of German assistance. But counting on German support did not equate support for either Germany or the Central Powers in the IRB/Volunteers. One of the IRB's organizers Albert Cotton summed up the geostrategic thinking behind the Rising:
if Germany won the war we would gain our objective -an Irish republic; but if Britain won our sustained revolt would have strengthened our position so much that we could hardly fail to get a hearing at the peace conference, and would obtain at least dominion status for all Ireland.
Some of the IRB/Volunteers would use the promise of German support, which much of the leadership knew was not coming, to stiffen up support among the rank and file to make the leap towards the Rising. Both Thomas MacDonagh and Sean MacDerment summoned up images of German successes and support after the Rising to convince foot-draggers that the Rising would succeed despite the odds.
Despite the double-game with German support played by the likes of Cotton and Casemate, the panic and fear a German-backed Irilish revolt shaped the British reaction to the Rising. Zeppelin raids on eastern England coincided with the Rising, but beyond requests by the IRB for such raids, it is unclear if the two events had much of a connection beyond convenience. But in the minds of many British authorities, German moves in the North Sea and Irish rebellion were intimately connected. This made the repression of the Rising much harsher. Large numbers of executions and drumhead courts' martial were much easier for Britain to justify in a wartime milieu. Ironically, it was this overreaction that turned a good deal of Irish public opinion in favor of the Rising. Some of the Rising's leadership recognized the potential that the appearance of German support could have to burn any bridges towards Anglo-Irish reconciliation. The Rising's official proclamation thanked Ireland's "gallant allies In Europe," a thinly veiled reference to Germany. Patrick Pearse was even more explicit when he was captured, he included a postscript in a letter to his mother that the "German expedition which I was counting on actually set sail but was defeated by the British." This was used as evidence that the Rising colluded with the Germans, and it is likely Pearse included the postscript in this letter because he knew would be read by the British and he would be made a martyr.
Pearse himself had very little love in private for Germany or the thought of a German prince being on the throne of an independent Ireland, but he and the other Irish revolutionaries realized that German aid, both real and symbolic, could be used to aid the cause if Irish independence. For their part, the Germans had very little use for Ireland and beyond toying with supporting Irish schemes, and Germany never really put much stock into Irish independence. But, given the highly charged political atmosphere of Ireland that predated the World War, such half-hearted or non-existent support was able to influence events in manner far out of proportion of obsolete rifles or a seized ship.
Sources
Doerries, Reinhard R. Prelude to the Easter Rising: Sir Roger Casement in Imperial Germany. London: Frank Cass, 2000.
Foster, R. F. Vivid Faces: The Revolutionary Generation in Ireland, 1890-1923. New York: Norton, 2015.
Gibney, John. What if the guns had landed? Another version of the Easter Rising. http://www.rte.ie/centuryireland/images/uploads/further-reading/John_Gibney_-_What_if_the_guns_had_landed.pdf
Hennessey, Thomas. Dividing Ireland: World War I and Partition. London: Routledge, 2005.
Lee, Joseph. Kerry's Fighting Story, 1916-21. Cork: Mercier Press, 2009.
McGarry, Fearghal. The Rising: Ireland--Easter 1916. Oxford: Oxford University Press, 2010.