 Complete the following phrase:  The 15th Derbyshire Battalion was a 1st-Line Territorial Army formation originally serving with the 148th Infantry Brigade, part of the 49th West Riding Infantry Division. However, in December 1939, the battalion was reassigned to the 25th Infantry Brigade and saw service with the BEF in France and Belgium in 1940 and being evacuated at Dunkirk. In late 1940, it was again reassigned to the 55th Infantry Brigade, 18th Infantry Division. The battalion, along with the rest of the 18th Division, was posted to Malaya to defend the peninsula and the island of Singapore against the Japanese. After 