Final answer:
The Supreme Court in the case of Gard Marine & Energy Limited v China National Chartering Co Ltd had to determine if the charterers were liable for breach of contract for not trading the vessel between safe ports.
Step-by-step explanation:
The main issue that the Supreme Court had to decide in the case of Gard Marine & Energy Limited v China National Chartering Co Ltd was A. Whether the charterers were liable for breach of contract for failing to trade the vessel only between safe ports. This question revolves around the interpretation of a shipping contract and the responsibilities and liabilities of the charterers, particularly in terms of ensuring the safety of the ports between which the vessel was traded. The judgment in this case would have significant implications for the shipping industry, influencing the contractual obligations and risk management strategies of the parties involved.