Complex sentence: Even before final testing had taken place in February 1944, an order for 2,100 Sherman tanks armed with 17-pounder guns was placed as the Challenger program was suffering constant delays and it was realised that few would be ready for Normandy.
Split into simpler sentences: Even before final testing had taken place in February 1944, an order for 2,100 Sherman tanks armed with 17-pounder guns was placed. The order was forthcoming as the Challenger program was suffering constant delays and it was realised that few would be ready for Normandy.