The Sea King Mk50 was the first fully uprated version of the Sea King HAS.1 to fly (30 Jun 1974), incorporating many features of the RN HAS.2. Ten were ordered by Australian Navy, with deliveries from Autumn 1974. RAN Sea King serials are N16- plus the Westland airframe build number (as opposed to the c/n). Sea King Mk.50 replaced the Westland Wessex HAS.31 as the RAN's ASW Helicopter.