Complex sentence: In addition to interfering with tank production goals, the bombing forced a steep drop in the production of spare parts, which as a percentage of tank production dropped from 25--30 percent in 1943 to 8 percent in the autumn of 1944.
Split into simpler sentences: In addition to interfering with tank production goals, the bombing forced a steep drop in the production of spare parts. Spare parts as a percentage of tank production dropped from 25--30 percent in 1943, to 8 percent in the autumn of 1944.