Complex sentence: On 30 June 1944, the four training divisions, had a combined total of 22,355 men, of which only about 1,100 were immediately available as replacements for the 21st Army Group.
Split into simpler sentences: On 30 June 1944, the four training divisions had a combined total of 22,355 men. Of this number, about only 1,100 were immediately available as replacements for the 21st Army Group.