Complex sentence: In the next 20 months, mines delivered by aircraft sank or damaged 164 Axis ships with the loss of 94 aircraft which still paled in comparison to the impact German mines had British shipping.
Split into simpler sentences: In the next 20 months, mines delivered by aircraft sank or damaged 164 Axis ships with the loss of 94 aircraft. Nevertheless, this paled in comparison to the impact German mines had on British shipping.