Complex sentence: Bligh was anxious to depart quickly, to reach Cape Horn before the end of the short southern summer, but the Admiralty did not accord him high priority, and delayed issuing the orders for a further three weeks.
Split into simpler sentences: Bligh was anxious to depart quickly, to reach Cape Horn before the end of the short southern summer. However, the Admiralty did not accord him high priority, and delayed issuing the orders for a further three weeks.