Complex sentence: Once the U.S. declared war, he enlisted in the US Air Corps and went into pilot training then sent to England in 1943, to the Base in Kimbolton as part of the 379th Bombardment Group (heavy).
Split into simpler sentences: Once the U.S. declared war, he enlisted in the US Air Corps and went into pilot training. He was sent to England in 1943, to the Base in Kimbolton as part of the 379th Bombardment Group (heavy).