Complex sentence: Altogether, the formation numbered eventually about 13,000 enlisted soldiers, 2600 NCOs and 580 officers of all grades, when it was sworn in by Gen. Sikorski on May 25,1940, shortly before arriving at the front in Lorraine.
Split into simpler sentences: Altogether, the unit had approximately 13,000 enlisted soldiers, 2600 NCOs and 580 officers of all grades. They were sworn in by the Gen. Sikorski on May 25,1940, shortly before arriving at the front line in Lorraine.