Forewarning: this post is mostly outsourced. For background you’ll want to read Michael Collins Dunn’s account of the Second Battle of Kut from late February. April 1916’s First Battle of Kut, as we know, was a complete Ottoman victory and one of the low points for Britain in the whole war. Following that disaster, the British army replaced its commander in Mesopotamia, Lt. General Percy Lake, with newly arrived (from Gallipoli) corps commander, Lt. General Frederick Stanley Maude.
Maude wisely spent the rest of 1916 repairing the damage that had been done in the campaign that culminated at Kut. He recruited new troops from India, trained them, and had his engineers build out a rail network that could support a full-scale northern offensive. His target was Baghdad. At this particular point in history Baghdad was really of no great military significance, but it was a high profile target whose capture would be a morale booster for the British war effort. Plus, just advancing that far north would put Maude’s army in position to threaten important Ottoman positions in northern Iraq and Anatolia, like Mosul.
As Dunn notes, the “Second Battle” of Kut wasn’t much of a battle. The Ottomans were damn sure not going to repeat Charles Townsend’s mistake of the year before and allow themselves to be bottled up there, so they withdrew north on February 24 without much resistance. Baghdad fell pretty much the same way:
Maude marched his main force up the east bank of the Tigris, arriving March 8 at the banks of its big tributary the Diyala. With the Turks defending the opposite banks of the Diyala, Maude moved most of his force downstream and crossed to the west bank of the Tigris. Detecting the movement (both sides had aircraft now with Germans flying for the Turks), Khalil moved most of his force to the west bank, leaving one regiment on the Diyala. The British soon pushed this aside, and Khalil, facing British advances on both banks, resolved on a retreat from Baghdad. By the evening of March 10, the Ottoman evacuation of Baghdad was under way, with no major battle having been fought.
Khalil Pasha made straight for Mosul, where he set up a defense and prepared for a British attack that…never came. Maude, wanting to avoid Townsend’s biggest mistake–overextending his supply lines–decided to stop his advance at Baghdad and take the necessary logistical steps to properly support the next phase of his advance. Then he up and died of cholera in November. At that point the Brits decided to shut down their Mesopotamian operations for the winter.
In 1918, the Levant front was where the action was, and the British Mesopotamian army was ordered to send part of its force west to help with that effort. Then, of course, the war ended. Although the Mesopotamian army eventually entered Mosul in November 1918, that was after the Armistace of Mudros had put the Ottomans out of the war, and the post-war status of the city had to be ironed out later.