A Mate is a high-ranking commissioned officer on board a ship, typically a merchant ship.

Name of the rank

A first (second, third etc.) mate may also be referred to as a first (second…) lieutenant or a first officer. Historically, the appellation “First lieutenant” was used by the Royal Navy, while the appellation “First mate” was preferred by merchant ships (including ships owned by the East India Company). The appellation “First Officer” seems to have been more common in the US. Today, first mate (or chief mate) and first lieutenant tend to be separate ranks.

The word mate may also refer to the assistant of a specialised warrant officer, see Mate (Petty Officer).

Position within the hierarchy

As the alternative name suggests, mates commonly held the rank of lieutenant. A ship would be assigned a number of lieutenants based on her size and these would be rated first, second, third etc. A first-rate ship (i.e. the largest type) would have six lieutenants, a small merchant ship may have only one or even none.

Most mates started out as midshipmen at a young age and would advance to lieutenant after passing the examination for lieutenant. Field promotions of midshipmen were possible.

A first mate would be the Captain’s second in command and would automatically be considered Acting Captain in the case of the Captain’s death. As such, the mates were the highest ranking officers after the Captain [1].


As having served as a mate was a prerequisite for becoming a captain, the mates would usually take take on similar tasks. Mates would lead watches, order manoeuvres, chart courses etc. They would be expected to command the ship during their watch without conferring with the captain about every decision. As such, a mate was already expected to know about navigation and seamanship. A mate would not be expected to actually take part in any of the manual labour on board a ship, but would be expected to know how to it was done.

Aboard the Obra Dinn

The Obra Dinn had four mates during her last voyage, an unusually large amount for a ship her size, which would commonly have had only one mate. They were:

All four perished during the Obra Dinn’s last voyage.


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