USS: United States Ship. Commissioned warships of the US Navy crewed by active duty US Navy personnel.
USNS: United States Naval Ship. Commissioned auxiliaries of the US Navy crewed by US Merchant Marine officers and crew.
M/V: Motor vessel (This is what the Minnow should have been called because it was powered by diesel engines. The “M/V Minnow”. To cause further confusion, M.V. also stands for ‘marine vessel’ in Canada.)
TS: Training Ship. Training-Class British War ships of the Royal Navy.
HMS: Her Majesty’s Ship. British War ships of the Royal Navy.
S/V: Sailing vessel.
NS: Nuclear-powered ship.
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Edited by me for readability, sourced from the Wikipedia article foot notes.