Complex sentence: In June 1940, the camp was named Oflag II D Gross-Born, and soon afterwards, French Army officers were brought to it in such numbers that in early 1941 there were 3731 of them.
Split into simpler sentences: In June 1940, the camp was named Oflag II D Gross-Born, and soon afterwards, French Army officers came. Altogether, in in early 1941 there were 3731 of them.