Complex sentence: It took until 1939 to bring the A12 Matilda II into production and it had not gone into service when the war began and the small turret ring of the Matilda made it impossible to replace the 2-pounder with a bigger gun.
Split into simpler sentences: It took until 1939 to bring the A12 Matilda II into production and it had not gone into service when the war began. The small turret ring of the Matilda made it impossible to replace the 2-pounder with a bigger gun.