The troops landed so that they could destory the forts so that the Navy could pass the Narrows so that they could bombard Constantinople so that the Turks would surrender so that supplies could reach Russia so that Russia would not collapse. All quite simple really!
The Ottoman Empire entered the First World War on the side of Germany and Austria. By early 1915 the front in France had reached stalemate. The British and French were keen to send supplies and reinforcements to their Russian allies, who had suffered a severe defeat at the Battle of Tannenberg.
There was only one small problem – the Ottomans held the narrow seaway know as the Dardanelles – the only ice-free route to Russia. Everyone knew that Turkey was "the Sick Man of Europe" and a show of force by the Royal Navy would make them see sense. Unfortunately the Turks thought otherwise and sank several British and French battleships when they tried to force the Dardanelles against forts and minefields.
In response the Imperial War Council in London, spurred on by Winston Churchill, the First Sea Lord, devised an amphibious invasion of the Gallipoli peninsula. The plan was to overrun the forts from the rear and clear the way for the fleet. However, this was definitely to be a side show — the main game was in France. Accordingly the British only sent one regular division, a partially equipped division of unemployed sailors, and a Corps of semi-trained and probably unreliable colonials – the ANZACs. The French for their part sent Colonial Troops. Again, everyone "knew" that the Turks were inferior and would run when faced by British Cold Steel.
For their part, the Turkish army had lost most of their artillery in the Balkan Wars of 1912-13, but these same wars had given them recent experience and solid training. More importantly, this was their country. Their senior command was reinforced with many excellent German officers.
On 25 April, 1915, an hour before dawn, in complete silence, the Anzacs rowed ashore near Ari Burnu, in a cove that would become known as Anzac Cove. The Royal Navy had landed them in the wrong place! Huge dirt cliffs and scrub-choked washouts. Nevertheless inland they went, overrunning the Turkish pickets, only to become hopelessly confused by the night landing, jigsaw terrain, inexperience, and a heroic Turkish counter-attack. Several miles inland, an especially gifted Turkish Officer – Mustafa Kemal, was reviewing his regiment after night maneuvers above Ari Burnu. Kemal's quick reaction saved the day for the Ottomans and launched him on his way to becoming the Founder of Modern Turkey. His 57th Regiment is as famous in Turkey as the Anzacs are in Australia and New Zealand.
Further South the regulars of the 29th Division landed on wired beaches. In the ensuing firestorm the Lancashires won "Six VC's before Breakfast," eventually pushing inland.
Three nations were born that day — Turkey, Australia and New Zealand.
The Entente never reached their first day's objectives, although the Turks only avoided defeat by a hair's breadth. Eventually, after nine months and half a million dead on both sides, they evacuated completely in one night.
The goal of the Entente was to remove all coastal defence artillery from the Western side of the Dardanelles, i.e. from the Eastern side of the peninsula. There were two types of coastal defence artillery – the fixed fortifications, chiefly on the Kilid Bahr plateau; and the mobile Howitzers of the 8th Heavy Artillery Regiment. The mobile howitzers were located on the ridges and in the steep valleys on the eastward side – Tenger Dere, Komuz Dere and Sogali Dere. The historical British plan called for complete occupation of the peninsula south of Mal Tepe.
The main force was the reinforced 29th Division, in practise operating as a small Corps. The Division was to land at the toe of the peninsula and then advance in a line across the peninsula and occupy the Kilid Bahr plateau. The Anzacs were to guard the flank and engage the reserves – their assigned goal (Mal Tepe) was known to be in the middle of the 9th Division's camp. The French and Royal Navy Division were to initially stage diversions and thereby pull strategic reserves away from the main landings. After the initial diversions they formed the reserve for the whole force.
Both the 29th Division and Anzacs had two-day plans. Day one was to land and establish a viable perimeter, day two was an advance to their strategic goals (Mal Tepe and Kilid Bahr respectively). For both landings, one or two brigades were allocated the task of the landing and securing a small beachhead. The remaining brigades were to land in good order, pass through and press on to the day's objective. The Anzac landing was concentrated in one area, the Helles landing was widely dispersed.
The Ottoman plan was to defend the peninsula in its entirety. The coast was completely covered with platoon and section pickets from 26th and 27th Regiments of the 19th Division, linked by telephone to the Divisional reserve (25th Regiment), and the Corps reserve (9th Division). The initial pickets were to report the invasion and hold the line while waiting for reinforcements. The regimental reserve was ordered to immediately reinforce and, if possible, counter-attack. The Corp reserve was to be committed when the enemy's intentions were clearly identified, and then counter-attack and drive the invaders back into the sea.