Complex sentence: However, the overall effect in the actual war was evaluated rather minor by staff officers, and so only a small program of converting merchant vessels to auxiliary cruisers was hastily brought under way on 5 September 1939.
Split into simpler sentences: However, the overall effect in the actual war was evaluated rather minor by staff officers. And so only a small program of converting merchant vessels to auxiliary cruisers was hastily brought under way on 5 September 1939.