For the day fighters of the Luftwaffe, the dominant reality in the period 1943-1945 was the massive growth in the daylight bombing raids of Germany by the United States. While other theatres did have a call on the fighter wings, by far and away the bulk of German day fighters in this period was employed in the air defence of Germany. The core of the day fighter units continued to be built around later variants of the BF-109 and the FW-190, which were being continually modified and upgraded with new armament combinations and employing new tactics to force down the U.S. heavy bombers.