In World War II only 17 Fusilier Battalions were formed: many battalions were given new functions - for example the 10th Battalion became a searchlight regiment, and others became anti-aircraft, anti-tank or reconnaissance units. Fusiliers regretted the changes but quickly came to see their value.

The 2nd Battalion were engaged throughout the withdrawal through Belgium and France where the remnants were evacuated from Dunkirk.
The 1st, 8th and 9th Battalions were active in the Middle Eastern and African campaign and in the Italian campaign. The 1st and 2nd Battalions fought almost alongside each other at the Battle of Monte Cassino in 1943, reunited for the first time since 1919.