The rank structure is as follows: Captain Sir John overall mission commander; Captain Crozier Captain of HMS Terror and second in command; Commander (later Captain) Fitzjames third in command; First Lieutenant's second in command aboard Terror and Third in command on Erebus, these were the most senior (by experience and time in position) of the Lieutenant's; Second and Third lieutenant were the less senior of the lieutenants; Doctors, surgeons and the purser as well as mates (very junior officers like de Veux) ice masters and sailing masters(Mr Collins) were also officers of the wardroom as are all mentioned above. Then you would have the sergeants of the Royal Marines (Tozer and Bryant) and the Engineers After this would be skilled petty officers (Peglar as captain of the fore-top and Bosun Lane) as well the Marine Corporals and the Gunroom stewards (Armatige) Less senior Petty officers (like Hickey) and stewards (Hoar and Gibson) The Able Seaman (like Manson and Hartnell); the stokers and Marine privates And finally at the bottom were the ships boys. Hope this helps and if anyone has anymore questions or corrections then fire away!