Complex sentence: Carson resorted to an archaic legal device called a petition of right against the Crown to bring the matter before the courts, as becoming a cadet excluded Archer-Shee from civil trial, but he had not reached the status for court-martial.
Split into simpler sentences: Carson resorted to an archaic legal device called a petition of right against the Crown to bring the matter before the courts. This was beacuse becoming a cadet excluded Archer-Shee from civil trial, but he had not reached the status for court-martial.