Complex sentence: The result, even with this heavy warhead, was that a much smaller airframe was needed to carry the required fuel-so small that the design could be portable and launched from a modified 88 mm Flak gun mounting.
Split into simpler sentences: The result, even with this heavy warhead, was that a much smaller airframe was needed to carry the required fuel. So small in fact that the design could be portable and launched from a modified 88mm Flak gun mounting.