Complex sentence: In February 1917,6th Mounted Brigade joined the Imperial Mounted Division and took part in the First and Second Battles of Gaza, they later transferred to the Yeomanry Mounted Division in June 1917, for the Third Battle of Gaza and the Battle of Beersheba.
Split into simpler sentences: In February 1917,6th Mounted Brigade joined the Imperial Mounted Division and took part in the First and Second Battles of Gaza. I, June 1917, it was transferred to the Yeomanry Mounted Division for the Third Battle of Gaza and the Battle of Beersheba.