This frock coat of a midshipman is quite similar to the lieutenant's undress frock. However, the sleeves feature a white boot cuff divided by a three-pointed flap of blue wool. This was known as the 'mariner's cuff' and came directly from the occupational dress of sailors. By the mid-18th century it was also incorporated into fashionable dress, featuring on both men's suit coats and women's riding habits.

The midshipman's frock also features a stand up collar of blue wool lined with white velvet, which would often have been removed and re-attached. For example, in cold or inclement weather, the collar would have been sewn on to the coat as a stand-up collar. If it was not needed in this way it could be re-attached as a turn-down collar. This was standard practice with most 18th-century clothing - lace and buttons were constantly being removed from one garment and re-applied to another. The midshipman would have been no stranger to stitching.