Complex sentence: He bitterly regrets leaving the army, his service in which took him to Malaya and in which he achieved the rank of Corporal, and he nearly always wears a workman's belt adorned with army cap badges.
Split into simpler sentences: He bitterly regrets leaving the army; his army service took him to Malaya and he achieved the rank of Corporal. He nearly always wears a workman's belt adorned with army cap badges.