Complex sentence: Horn and Wyczynski 2003, p.270 On 11 August 1943 the 1st Canadian Parachute Battalion arrived in England and was assigned to the brigade, and the 7th Battalion was transferred to the 5th Parachute Brigade which was in the process of forming.
Split into simpler sentences: Horn and Wyczynski 2003, p.270 Then on 11 August 1943, the 1st Canadian Parachute Battalion arrived in England and was assigned to the brigade. To accommodate them the 7th Battalion was transferred to the 5th Parachute Brigade, which was still in the process of forming.