I thought of sending you and AgroDavid a private email asking if you knew any cranky old men who just happened to have served as officers in RAN. It's not about the Australian Navy. It's about an RAN officer 'transferred' to a very foreign service and dealing with, among other things, the differences in speech patterns, the way things are named, etc. The setting is Thinking Horndog's Swarm Cycle which I know summat about, it's just the way the character would talk that I can't fake.
You raise an excellent example. The US Navy has a title "First Lieutenant". It refers to the officer responsible for the First (or "Deck") Division, all those guys who deal with all the deck equipment. Boats, anchors, the flagstaff, etc. Anyone raised in the USN would hear Our Hero say "I was First Lieutenant on...." and think he was an established expert on anchor maintenance. Our Hero would be saying "If the Old Man buys it I'm in command", something completely different. I need a translator!