1 July 1916: The Battle of the Somme in France began on this day. The battle marked the beginning of the British Army’s summer Offensive against the German forces opposed to them.
The Germans were very well dug in and despite a week long bombardment their entrenchments were still more or less intact. Many soldiers from Ireland took part in this bloody battle - the most costly day in the history of the British Army.

One of the most successful operations that day was by the men of the 36th Ulster Division.

‘The 36th Ulster Division's sector of the Somme lay astride the marshy valley of the river Ancre and the higher ground south of the river. Their task was to cross the ridge and take the German second line near Grandcourt. In their path lay not only the German front line, but just beyond it, the intermediate line within which was the Schwaben Redoubt.

The First Day of the Somme was the anniversary (Julian Calendar) of the Battle of the Boyne, a fact remarked on by the leaders of the Division. Stories that some men went over the top wearing orange sashes are, however, thought to be myths.

On 1 July, following the preliminary bombardment, the Ulstermen quickly took the German front line. But intelligence was so poor that, with the rest of the division attacking under creep bombardment (artillery fired in front or over men; they advance as it moves), the Ulstermen would have come under attack from their own bombardment at the German first line.

But they still advanced, moving to the crest so rapidly that the Germans had no time to come up from their dugouts (generally 30–40 feet below ground) in the Schwaben Redoubt, which was also taken. So successful was the advance that by 10:00 some had reached the German second line. But again they came under their own barrage, not due to finish until 10:10. However, this successful penetration had to be given up before nightfall, as it was unmatched by those at its flanks. The Ulstermen were exposed in a narrow salient, open to attack on three sides. They were running out of ammunition and supplies, and a full German counter-attack at 22:00 forced them to withdraw, giving up virtually all they gained.'
http://en.wikipedia.org/wiki/36th_(Ulster)_Division#36th_Ulster_Division.2C_Somme

While the Ulstermen had at least the satisfaction of achieving their initial goals the sad fate of the Tyneside Irish Brigade  was indicative of what was happening up and down the Front as the assaults of so many battalions were thrown back with appalling casualties.

'The Tyneside Irish Brigade was a British First World War infantry brigade of Kitchener's Army, raised in 1914. Officially numbered the 103rd (Tyneside Irish) Brigade, it contained four Pals battalions from Newcastle-upon-Tyne, largely made up of men of Irish extraction. (Another Newcastle brigade — the 102nd (Tyneside Scottish) — contained Tynesiders with Scottish connections).

The brigade's four battalions were known as the 1st to 4th Tyneside Irish. When taken over by the British Army, these became battalions of the Northumberland Fusiliers.

1st Tyneside Irish (24th Battalion, Northumberland Fusiliers).
2nd Tyneside Irish (25th Battalion, Northumberland Fusiliers).
3rd Tyneside Irish (26th Battalion, Northumberland Fusiliers).
4th Tyneside Irish (27th Battalion, Northumberland Fusiliers).
Along with the 101st and 102nd Brigades, the Tyneside Irish made up the 34th Division which arrived in France in January 1916 and first saw action in the Battle of the Somme that year. On the first day on the Somme, the 34th Division attacked astride the Albert-Bapaume road at La Boisselle. The brigade's task was to follow up the main attack by the 101st and 102nd Brigades and advance on a line from Pozières to Contalmaison.

Advancing at the same time as the main attack, the brigade started from the reserve trenches on the Tara-Usna Line. The four battalions, marching in extended line (from left to right; the 2nd, 3rd, 1st and 4th), advanced down into Avoca Valley and then up the other side to the British front-line trench. From there they had to cross no man's land, pass through the German front-line and advance to their objectives. However, the main attack was an almost complete failure and the Tyneside Irish were utterly exposed to the machine guns of the German defences. The brigade suffered heavy casualties even before its battalions reached the British front-line. Opposite La Boisselle the brigade was halted but on the right, elements of the 1st and 4th battalions were able to advance up 'Sausage Valley' and pass through the German front-line. Two small parties met up behind the German support trench and pushed on towards their objective of Contalmaison. Their effort was in vain as they were eventually killed or captured.

The 1st battalion suffered 620 casualties on 1 July (18 officers and 602 other ranks), its commander, Lieutenant Colonel L.M. Howard, was among the dead. The 4th battalion suffered 539 casualties (20 officers and 519 other ranks). While the commanders of the 2nd and 3rd battalions were both wounded, as was the Brigade commander, Brigadier General N.J.G. Cameron.’
http://en.wikipedia.org/wiki/103rd_(Tyneside_Irish)_Brigade