I see, I can use that advice, thanks! Of other ranks, who amongst them would be a PO? That involves specialisation and command doesn't it?
Also, if you don't mind me asking, what do we make of Spacehands or POs who are navigators and pilots?? That always made me wonder, particularly when many ship descriptions say the captain and pilot are one and the same ...
First, using US ranks, a "PO" is a Petty Officer"... the Navy way of saying "NCO"... Non-commissioned Officer.
An E-4 (Corporal) is a Petty Officer 3rd, an E-5 (sergeant) a PO-2, an E-6 a PO-1, an E-7 a Chief PO, E-8 = Senior CPO, E-9 = Master CPO.
Second, up to and into WW2 it was common in the USMC, USN, and USAAC/USAAF to have E-4/5/6s taken from the technical branches (usually aircraft mechanics) and trained as pilots and navigators, while retaining their NCO/PO rank.
It was actually interesting to find a Marine Staff Sergeant acting as PIC (Pilot in Command) with a 1Lt (Lt JG) as co-pilot, due to the SSGT having more flight hours in the type.
This was more common in fighters, 1/2-man attack aircraft, and transports... bombers were virtually always commanded/flown by officers.
During the latter stages of WW2, nearly all such enlisted pilots/navigators received commissions as normal officers, and after the war all pilots/navigators had to be commissioned officers before entering training (except for a select few "Warrant Officer" pilots... usually Army helicopter pilots).
Warrant Officers are enlisted selected for promotion to a quasi-officer status... to gain the benefit of their technical expertise in a position of authority & responsibility without having to make them "real officers".
Crew sizes of small ocean-going military vessels:
WW1 Submarine Chasers (85 tons) had 2 officers and 24 enlisted.
The WW1 Eagle class Patrol craft (615 tons) had a crew of 5 officers and 56 enlisted.
So figure 1 officer for each 10-12 enlisted crew.