Complex sentence: A conventional strategic bombing campaign was out of the question because industrial targets in Japan were well beyond the range of even the largest strategic bombers operating from bases in Australia and New Guinea, and the results of the effort against the January convoy were very disappointing.
Split into simpler sentences: A conventional strategic bombing campaign was out of the question because industrial targets in Japan were well beyond the range of even the largest strategic bombers operating from bases in Australia and New Guinea. But the results of the effort against the January convoy were very disappointing.